SUBROUTINE DDASSL (RES, NEQ, T, Y, YPRIME, TOUT, INFO, RTOL, ATOL, + IDID, RWORK, LRW, IWORK, LIW, RPAR, IPAR, JAC) C***BEGIN PROLOGUE DDASSL C***PURPOSE This code solves a system of differential/algebraic C equations of the form G(T,Y,YPRIME) = 0. C***LIBRARY SLATEC (DASSL) C***CATEGORY I1A2 C***TYPE DOUBLE PRECISION (SDASSL-S, DDASSL-D) C***KEYWORDS DIFFERENTIAL/ALGEBRAIC, BACKWARD DIFFERENTIATION FORMULAS, C IMPLICIT DIFFERENTIAL SYSTEMS C***AUTHOR PETZOLD, LINDA R., (LLNL) C COMPUTING AND MATHEMATICS RESEARCH DIVISION C LAWRENCE LIVERMORE NATIONAL LABORATORY C L - 316, P.O. BOX 808, C LIVERMORE, CA. 94550 C***DESCRIPTION C C *Usage: C C EXTERNAL RES, JAC C INTEGER NEQ, INFO(N), IDID, LRW, LIW, IWORK(LIW), IPAR C DOUBLE PRECISION T, Y(NEQ), YPRIME(NEQ), TOUT, RTOL, ATOL, C * RWORK(LRW), RPAR C C CALL DDASSL (RES, NEQ, T, Y, YPRIME, TOUT, INFO, RTOL, ATOL, C * IDID, RWORK, LRW, IWORK, LIW, RPAR, IPAR, JAC) C C C *Arguments: C (In the following, all real arrays should be type DOUBLE PRECISION.) C C RES:EXT This is a subroutine which you provide to define the C differential/algebraic system. C C NEQ:IN This is the number of equations to be solved. C C T:INOUT This is the current value of the independent variable. C C Y(*):INOUT This array contains the solution components at T. C C YPRIME(*):INOUT This array contains the derivatives of the solution C components at T. C C TOUT:IN This is a point at which a solution is desired. C C INFO(N):IN The basic task of the code is to solve the system from T C to TOUT and return an answer at TOUT. INFO is an integer C array which is used to communicate exactly how you want C this task to be carried out. (See below for details.) C N must be greater than or equal to 15. C C RTOL,ATOL:INOUT These quantities represent relative and absolute C error tolerances which you provide to indicate how C accurately you wish the solution to be computed. You C may choose them to be both scalars or else both vectors. C Caution: In Fortran 77, a scalar is not the same as an C array of length 1. Some compilers may object C to using scalars for RTOL,ATOL. C C IDID:OUT This scalar quantity is an indicator reporting what the C code did. You must monitor this integer variable to C decide what action to take next. C C RWORK:WORK A real work array of length LRW which provides the C code with needed storage space. C C LRW:IN The length of RWORK. (See below for required length.) C C IWORK:WORK An integer work array of length LIW which probides the C code with needed storage space. C C LIW:IN The length of IWORK. (See below for required length.) C C RPAR,IPAR:IN These are real and integer parameter arrays which C you can use for communication between your calling C program and the RES subroutine (and the JAC subroutine) C C JAC:EXT This is the name of a subroutine which you may choose C to provide for defining a matrix of partial derivatives C described below. C C Quantities which may be altered by DDASSL are: C T, Y(*), YPRIME(*), INFO(1), RTOL, ATOL, C IDID, RWORK(*) AND IWORK(*) C C *Description C C Subroutine DDASSL uses the backward differentiation formulas of C orders one through five to solve a system of the above form for Y and C YPRIME. Values for Y and YPRIME at the initial time must be given as C input. These values must be consistent, (that is, if T,Y,YPRIME are C the given initial values, they must satisfy G(T,Y,YPRIME) = 0.). The C subroutine solves the system from T to TOUT. It is easy to continue C the solution to get results at additional TOUT. This is the interval C mode of operation. Intermediate results can also be obtained easily C by using the intermediate-output capability. C C The following detailed description is divided into subsections: C 1. Input required for the first call to DDASSL. C 2. Output after any return from DDASSL. C 3. What to do to continue the integration. C 4. Error messages. C C C -------- INPUT -- WHAT TO DO ON THE FIRST CALL TO DDASSL ------------ C C The first call of the code is defined to be the start of each new C problem. Read through the descriptions of all the following items, C provide sufficient storage space for designated arrays, set C appropriate variables for the initialization of the problem, and C give information about how you want the problem to be solved. C C C RES -- Provide a subroutine of the form C SUBROUTINE RES(T,Y,YPRIME,DELTA,IRES,RPAR,IPAR) C to define the system of differential/algebraic C equations which is to be solved. For the given values C of T,Y and YPRIME, the subroutine should C return the residual of the defferential/algebraic C system C DELTA = G(T,Y,YPRIME) C (DELTA(*) is a vector of length NEQ which is C output for RES.) C C Subroutine RES must not alter T,Y or YPRIME. C You must declare the name RES in an external C statement in your program that calls DDASSL. C You must dimension Y,YPRIME and DELTA in RES. C C IRES is an integer flag which is always equal to C zero on input. Subroutine RES should alter IRES C only if it encounters an illegal value of Y or C a stop condition. Set IRES = -1 if an input value C is illegal, and DDASSL will try to solve the problem C without getting IRES = -1. If IRES = -2, DDASSL C will return control to the calling program C with IDID = -11. C C RPAR and IPAR are real and integer parameter arrays which C you can use for communication between your calling program C and subroutine RES. They are not altered by DDASSL. If you C do not need RPAR or IPAR, ignore these parameters by treat- C ing them as dummy arguments. If you do choose to use them, C dimension them in your calling program and in RES as arrays C of appropriate length. C C NEQ -- Set it to the number of differential equations. C (NEQ .GE. 1) C C T -- Set it to the initial point of the integration. C T must be defined as a variable. C C Y(*) -- Set this vector to the initial values of the NEQ solution C components at the initial point. You must dimension Y of C length at least NEQ in your calling program. C C YPRIME(*) -- Set this vector to the initial values of the NEQ C first derivatives of the solution components at the initial C point. You must dimension YPRIME at least NEQ in your C calling program. If you do not know initial values of some C of the solution components, see the explanation of INFO(11). C C TOUT -- Set it to the first point at which a solution C is desired. You can not take TOUT = T. C integration either forward in T (TOUT .GT. T) or C backward in T (TOUT .LT. T) is permitted. C C The code advances the solution from T to TOUT using C step sizes which are automatically selected so as to C achieve the desired accuracy. If you wish, the code will C return with the solution and its derivative at C intermediate steps (intermediate-output mode) so that C you can monitor them, but you still must provide TOUT in C accord with the basic aim of the code. C C The first step taken by the code is a critical one C because it must reflect how fast the solution changes near C the initial point. The code automatically selects an C initial step size which is practically always suitable for C the problem. By using the fact that the code will not step C past TOUT in the first step, you could, if necessary, C restrict the length of the initial step size. C C For some problems it may not be permissible to integrate C past a point TSTOP because a discontinuity occurs there C or the solution or its derivative is not defined beyond C TSTOP. When you have declared a TSTOP point (SEE INFO(4) C and RWORK(1)), you have told the code not to integrate C past TSTOP. In this case any TOUT beyond TSTOP is invalid C input. C C INFO(*) -- Use the INFO array to give the code more details about C how you want your problem solved. This array should be C dimensioned of length 15, though DDASSL uses only the first C eleven entries. You must respond to all of the following C items, which are arranged as questions. The simplest use C of the code corresponds to answering all questions as yes, C i.e. setting all entries of INFO to 0. C C INFO(1) - This parameter enables the code to initialize C itself. You must set it to indicate the start of every C new problem. C C **** Is this the first call for this problem ... C Yes - Set INFO(1) = 0 C No - Not applicable here. C See below for continuation calls. **** C C INFO(2) - How much accuracy you want of your solution C is specified by the error tolerances RTOL and ATOL. C The simplest use is to take them both to be scalars. C To obtain more flexibility, they can both be vectors. C The code must be told your choice. C C **** Are both error tolerances RTOL, ATOL scalars ... C Yes - Set INFO(2) = 0 C and input scalars for both RTOL and ATOL C No - Set INFO(2) = 1 C and input arrays for both RTOL and ATOL **** C C INFO(3) - The code integrates from T in the direction C of TOUT by steps. If you wish, it will return the C computed solution and derivative at the next C intermediate step (the intermediate-output mode) or C TOUT, whichever comes first. This is a good way to C proceed if you want to see the behavior of the solution. C If you must have solutions at a great many specific C TOUT points, this code will compute them efficiently. C C **** Do you want the solution only at C TOUT (and not at the next intermediate step) ... C Yes - Set INFO(3) = 0 C No - Set INFO(3) = 1 **** C C INFO(4) - To handle solutions at a great many specific C values TOUT efficiently, this code may integrate past C TOUT and interpolate to obtain the result at TOUT. C Sometimes it is not possible to integrate beyond some C point TSTOP because the equation changes there or it is C not defined past TSTOP. Then you must tell the code C not to go past. C C **** Can the integration be carried out without any C restrictions on the independent variable T ... C Yes - Set INFO(4)=0 C No - Set INFO(4)=1 C and define the stopping point TSTOP by C setting RWORK(1)=TSTOP **** C C INFO(5) - To solve differential/algebraic problems it is C necessary to use a matrix of partial derivatives of the C system of differential equations. If you do not C provide a subroutine to evaluate it analytically (see C description of the item JAC in the call list), it will C be approximated by numerical differencing in this code. C although it is less trouble for you to have the code C compute partial derivatives by numerical differencing, C the solution will be more reliable if you provide the C derivatives via JAC. Sometimes numerical differencing C is cheaper than evaluating derivatives in JAC and C sometimes it is not - this depends on your problem. C C **** Do you want the code to evaluate the partial C derivatives automatically by numerical differences ... C Yes - Set INFO(5)=0 C No - Set INFO(5)=1 C and provide subroutine JAC for evaluating the C matrix of partial derivatives **** C C INFO(6) - DDASSL will perform much better if the matrix of C partial derivatives, DG/DY + CJ*DG/DYPRIME, C (here CJ is a scalar determined by DDASSL) C is banded and the code is told this. In this C case, the storage needed will be greatly reduced, C numerical differencing will be performed much cheaper, C and a number of important algorithms will execute much C faster. The differential equation is said to have C half-bandwidths ML (lower) and MU (upper) if equation i C involves only unknowns Y(J) with C I-ML .LE. J .LE. I+MU C for all I=1,2,...,NEQ. Thus, ML and MU are the widths C of the lower and upper parts of the band, respectively, C with the main diagonal being excluded. If you do not C indicate that the equation has a banded matrix of partial C derivatives, the code works with a full matrix of NEQ**2 C elements (stored in the conventional way). Computations C with banded matrices cost less time and storage than with C full matrices if 2*ML+MU .LT. NEQ. If you tell the C code that the matrix of partial derivatives has a banded C structure and you want to provide subroutine JAC to C compute the partial derivatives, then you must be careful C to store the elements of the matrix in the special form C indicated in the description of JAC. C C **** Do you want to solve the problem using a full C (dense) matrix (and not a special banded C structure) ... C Yes - Set INFO(6)=0 C No - Set INFO(6)=1 C and provide the lower (ML) and upper (MU) C bandwidths by setting C IWORK(1)=ML C IWORK(2)=MU **** C C C INFO(7) -- You can specify a maximum (absolute value of) C stepsize, so that the code C will avoid passing over very C large regions. C C **** Do you want the code to decide C on its own maximum stepsize? C Yes - Set INFO(7)=0 C No - Set INFO(7)=1 C and define HMAX by setting C RWORK(2)=HMAX **** C C INFO(8) -- Differential/algebraic problems C may occaisionally suffer from C severe scaling difficulties on the C first step. If you know a great deal C about the scaling of your problem, you can C help to alleviate this problem by C specifying an initial stepsize HO. C C **** Do you want the code to define C its own initial stepsize? C Yes - Set INFO(8)=0 C No - Set INFO(8)=1 C and define HO by setting C RWORK(3)=HO **** C C INFO(9) -- If storage is a severe problem, C you can save some locations by C restricting the maximum order MAXORD. C the default value is 5. for each C order decrease below 5, the code C requires NEQ fewer locations, however C it is likely to be slower. In any C case, you must have 1 .LE. MAXORD .LE. 5 C **** Do you want the maximum order to C default to 5? C Yes - Set INFO(9)=0 C No - Set INFO(9)=1 C and define MAXORD by setting C IWORK(3)=MAXORD **** C C INFO(10) --If you know that the solutions to your equations C will always be nonnegative, it may help to set this C parameter. However, it is probably best to C try the code without using this option first, C and only to use this option if that doesn 'tC work very well.C **** Do you want the code to solve the problem withoutC invoking any special nonnegativity constraints?C Yes - Set INFO(10)=0C No - Set INFO(10)=1CC INFO(11) --DDASSL normally requires the initial T,C Y, and YPRIME to be consistent. That is,C you must have G(T,Y,YPRIME) = 0 at the initialC time. If you do not know the initialC derivative precisely, you can let DDASSL tryC to compute it.C **** Are the initialHE INITIAL T, Y, YPRIME consistent?C Yes - Set INFO(11) = 0C No - Set INFO(11) = 1,C and set YPRIME to an initial approximationC to YPRIME. (If you have no idea whatC YPRIME should be, set it to zero. NoteC that the initial Y should be suchC that there must exist a YPRIME so thatC G(T,Y,YPRIME) = 0.)CC RTOL, ATOL -- You must assign relative (RTOL) and absolute (ATOLC error tolerances to tell the code how accurately youC want the solution to be computed. They must be definedC as variables because the code may change them. YouC have two choices --C Both RTOL and ATOL are scalars. (INFO(2)=0)C Both RTOL and ATOL are vectors. (INFO(2)=1)C in either case all components must be non-negative.CC The tolerances are used by the code in a local errorC test at each step which requires roughly thatC ABS(LOCAL ERROR) .LE. RTOL*ABS(Y)+ATOLC for each vector component.C (More specifically, a root-mean-square norm is used toC measure the size of vectors, and the error test uses theC magnitude of the solution at the beginning of the step.)CC The true (global) error is the difference between theC true solution of the initial value problem and theC computed approximation. Practically all present dayC codes, including this one, control the local error atC each step and do not even attempt to control the globalC error directly.C Usually, but not always, the true accuracy of theC computed Y is comparable to the error tolerances. ThisC code will usually, but not always, deliver a moreC accurate solution if you reduce the tolerances andC integrate again. By comparing two such solutions youC can get a fairly reliable idea of the true error in theC solution at the bigger tolerances.CC Setting ATOL=0. results in a pure relative error test onC that component. Setting RTOL=0. results in a pureC absolute error test on that component. A mixed testC with non-zero RTOL and ATOL corresponds roughly to aC relative error test when the solution component is muchC bigger than ATOL and to an absolute error test when theC solution component is smaller than the threshhold ATOL.CC The code will not attempt to compute a solution at anC accuracy unreasonable for the machine being used. It willC advise you if you ask for too much accuracy and informC you as to the maximum accuracy it believes possible.CC RWORK(*) -- Dimension this real work array of length LRW in yourC calling program.CC LRW -- Set it to the declared length of the RWORK array.C You must haveC LRW .GE. 40+(MAXORD+4)*NEQ+NEQ**2C for the full (dense) JACOBIAN case (when INFO(6)=0), orC LRW .GE. 40+(MAXORD+4)*NEQ+(2*ML+MU+1)*NEQC for the banded user-defined JACOBIAN caseC (when INFO(5)=1 and INFO(6)=1), orC LRW .GE. 40+(MAXORD+4)*NEQ+(2*ML+MU+1)*NEQC +2*(NEQ/(ML+MU+1)+1)C for the banded finite-difference-generated JACOBIAN caseC (when INFO(5)=0 and INFO(6)=1)CC IWORK(*) -- Dimension this integer work array of length LIW inC your calling program.CC LIW -- Set it to the declared length of the IWORK array.C You must have LIW .GE. 20+NEQCC RPAR, IPAR -- These are parameter arrays, of real and integerC type, respectively. You can use them for communicationC between your program that calls DDASSL and theC RES subroutine (and the JAC subroutine). They are notC altered by DDASSL. If you do not need RPAR or IPAR,C ignore these parameters by treating them as dummyC arguments. If you do choose to use them, dimensionC them in your calling program and in RES (and in JAC)C as arrays of appropriate length.CC JAC -- If you have set INFO(5)=0, you can ignore this parameterC by treating it as a dummy argument. Otherwise, you mustC provide a subroutine of the formC SUBROUTINE JAC(T,Y,YPRIME,PD,CJ,RPAR,IPAR)C to define the matrix of partial derivativesC PD=DG/DY+CJ*DG/DYPRIMEC CJ is a scalar which is input to JAC.C For the given values of T,Y,YPRIME, theC subroutine must evaluate the non-zero partialC derivatives for each equation and each solutionC component, and store these values in theC matrix PD. The elements of PD are set to zeroC before each call to JAC so only non-zero elementsC need to be defined.CC Subroutine JAC must not alter T,Y,(*),YPRIME(*), or CJ.C You must declare the name JAC in an EXTERNAL statement inC your program that calls DDASSL. You must dimension Y,C YPRIME and PD in JAC.CC The way you must store the elements into the PD matrixC depends on the structure of the matrix which youC indicated by INFO(6).C *** INFO(6)=0 -- Full (dense) matrix ***C Give PD a first dimension of NEQ.C When you evaluate the (non-zero) partial derivativeC of equation I with respect to variable J, you mustC store it in PD according toC PD(I,J) = "DG(I)/DY(J)+CJ*DG(I)/DYPRIME(J)"C *** INFO(6)=1 -- Banded JACOBIAN with ML lower and MUC upper diagonal bands (refer to INFO(6) descriptionC of ML and MU) ***C Give PD a first dimension of 2*ML+MU+1.C when you evaluate the (non-zero) partial derivativeC of equation I with respect to variable J, you mustC store it in PD according toC IROW = I - J + ML + MU + 1C PD(IROW,J) = "DG(I)/DY(J)+CJ*DG(I)/DYPRIME(J)"CC RPAR and IPAR are real and integer parameter arraysC which you can use for communication between your callingC program and your JACOBIAN subroutine JAC. They are notC altered by DDASSL. If you do not need RPAR or IPAR,C ignore these parameters by treating them as dummyC arguments. If you do choose to use them, dimensionC them in your calling program and in JAC as arrays ofC appropriate length.CCC OPTIONALLY REPLACEABLE NORM ROUTINE:CC DDASSL uses a weighted norm DDANRM to measure the sizeC of vectors such as the estimated error in each step.C A FUNCTION subprogramC DOUBLE PRECISION FUNCTION DDANRM(NEQ,V,WT,RPAR,IPAR)C DIMENSION V(NEQ),WT(NEQ)C is used to define this norm. Here, V is the vectorC whose norm is to be computed, and WT is a vector ofC weights. A DDANRM routine has been included with DDASSLC which computes the weighted root-mean-square normC given byC DDANRM=SQRT((1/NEQ)*SUM(V(I)/WT(I))**2)C this norm is suitable for most problems. In someC special cases, it may be more convenient and/orC efficient to define your own norm by writing a functionC subprogram to be called instead of DDANRM. This should,C however, be attempted only after careful thought andC consideration.CCC -------- OUTPUT -- AFTER ANY RETURN FROM DDASSL ---------------------CC The principal aim of the code is to return a computed solution atC TOUT, although it is also possible to obtain intermediate resultsC along the way. To find out whether the code achieved its goalC or if the integration process was interrupted before the task wasC completed, you must check the IDID parameter.CCC T -- The solution was successfully advanced to theC output value of T.CC Y(*) -- Contains the computed solution approximation at T.CC YPRIME(*) -- Contains the computed derivativeC approximation at T.CC IDID -- Reports what the code did.CC *** Task completed ***C Reported by positive values of IDIDCC IDID = 1 -- A step was successfully taken in theC intermediate-output mode. The code has notC yet reached TOUT.CC IDID = 2 -- The integration to TSTOP was successfullyC completed (T=TSTOP) by stepping exactly to TSTOP.CC IDID = 3 -- The integration to TOUT was successfullyC completed (T=TOUT) by stepping past TOUT.C Y(*) is obtained by interpolation.C YPRIME(*) is obtained by interpolation.CC *** Task interrupted ***C Reported by negative values of IDIDCC IDID = -1 -- A large amount of work has been expended.C (About 500 steps)CC IDID = -2 -- The error tolerances are too stringent.CC IDID = -3 -- The local error test cannot be satisfiedC because you specified a zero component in ATOLC and the corresponding computed solutionC component is zero. Thus, a pure relative errorC test is impossible for this component.CC IDID = -6 -- DDASSL had repeated error testC failures on the last attempted step.CC IDID = -7 -- The corrector could not converge.CC IDID = -8 -- The matrix of partial derivativesC is singular.CC IDID = -9 -- The corrector could not converge.C there were repeated error test failuresC in this step.CC IDID =-10 -- The corrector could not convergeC because IRES was equal to minus one.CC IDID =-11 -- IRES equal to -2 was encounteredC and control is being returned to theC calling program.CC IDID =-12 -- DDASSL failed to compute the initialC YPRIME.CCCC IDID = -13,..,-32 -- Not applicable for this codeCC *** Task terminated ***C Reported by the value of IDID=-33CC IDID = -33 -- The code has encountered trouble from whichC it cannot recover. A message is printedC explaining the trouble and control is returnedC to the calling program. For example, this occursC when invalid input is detected.CC RTOL, ATOL -- These quantities remain unchanged except whenC IDID = -2. In this case, the error tolerances have beenC increased by the code to values which are estimated toC be appropriate for continuing the integration. However,C the reported solution at T was obtained using the inputC values of RTOL and ATOL.CC RWORK, IWORK -- Contain information which is usually of noC interest to the user but necessary for subsequent calls.C However, you may find use forCC RWORK(3)--Which contains the step size H to beC attempted on the next step.CC RWORK(4)--Which contains the current value of theC independent variable, i.e., the farthest pointC integration has reached. This will be differentC from T only when interpolation has beenC performed (IDID=3).CC RWORK(7)--Which contains the stepsize usedC on the last successful step.CC IWORK(7)--Which contains the order of the method toC be attempted on the next step.CC IWORK(8)--Which contains the order of the method usedC on the last step.CC IWORK(11)--Which contains the number of steps taken soC far.CC IWORK(12)--Which contains the number of calls to RESC so far.CC IWORK(13)--Which contains the number of evaluations ofC the matrix of partial derivatives needed soC far.CC IWORK(14)--Which contains the total numberC of error test failures so far.CC IWORK(15)--Which contains the total numberC of convergence test failures so far.C (includes singular iteration matrixC failures.)CCC -------- INPUT -- WHAT TO DO TO CONTINUE THE INTEGRATION ------------C (CALLS AFTER THE FIRST)CC This code is organized so that subsequent calls to continue theC integration involve little (if any) additional effort on yourC part. You must monitor the IDID parameter in order to determineC what to do next.CC Recalling that the principal task of the code is to integrateC from T to TOUT (the interval mode), usually all you will needC to do is specify a new TOUT upon reaching the current TOUT.CC Do not alter any quantity not specifically permitted below,C in particular do not alter NEQ,T,Y(*),YPRIME(*),RWORK(*),IWORK(*)C or the differential equation in subroutine RES. Any suchC alteration constitutes a new problem and must be treated as such,C i.e., you must start afresh.CC You cannot change from vector to scalar error control or viceC versa (INFO(2)), but you can change the size of the entries ofC RTOL, ATOL. Increasing a tolerance makes the equation easierC to integrate. Decreasing a tolerance will make the equationC harder to integrate and should generally be avoided.CC You can switch from the intermediate-output mode to theC interval mode (INFO(3)) or vice versa at any time.CC If it has been necessary to prevent the integration from goingC past a point TSTOP (INFO(4), RWORK(1)), keep in mind that theC code will not integrate to any TOUT beyond the currentlyC specified TSTOP. Once TSTOP has been reached you must changeC the value of TSTOP or set INFO(4)=0. You may change INFO(4)C or TSTOP at any time but you must supply the value of TSTOP inC RWORK(1) whenever you set INFO(4)=1.CC Do not change INFO(5), INFO(6), IWORK(1), or IWORK(2)C unless you are going to restart the code.CC *** Following a completed task ***C IfC IDID = 1, call the code again to continue the integrationC another step in the direction of TOUT.CC IDID = 2 or 3, define a new TOUT and call the code again.C TOUT must be different from T. You cannot changeC the direction of integration without restarting.CC *** Following an interrupted task ***C To show the code that you realize the task wasC interrupted and that you want to continue, youC must take appropriate action and set INFO(1) = 1C IfC IDID = -1, The code has taken about 500 steps.C If you want to continue, set INFO(1) = 1 andC call the code again. An additional 500 stepsC will be allowed.CC IDID = -2, The error tolerances RTOL, ATOL have beenC increased to values the code estimates appropriateC for continuing. You may want to change themC yourself. If you are sure you want to continueC with relaxed error tolerances, set INFO(1)=1 andC call the code again.CC IDID = -3, A solution component is zero and you set theC corresponding component of ATOL to zero. If youC are sure you want to continue, you must firstC alter the error criterion to use positive valuesC for those components of ATOL corresponding to zeroC solution components, then set INFO(1)=1 and callC the code again.CC IDID = -4,-5 --- Cannot occur with this code.CC IDID = -6, Repeated error test failures occurred on theC last attempted step in DDASSL. A singularity in theC solution may be present. If you are absolutelyC certain you want to continue, you should restartC the integration. (Provide initial values of Y andC YPRIME which are consistent)CC IDID = -7, Repeated convergence test failures occurredC on the last attempted step in DDASSL. An inaccurateC or ill-conditioned JACOBIAN may be the problem. IfC you are absolutely certain you want to continue, youC should restart the integration.CC IDID = -8, The matrix of partial derivatives is singular.C Some of your equations may be redundant.C DDASSL cannot solve the problem as stated.C It is possible that the redundant equationsC could be removed, and then DDASSL couldC solve the problem. It is also possibleC that a solution to your problem eitherC does not exist or is not unique.CC IDID = -9, DDASSL had multiple convergence testC failures, preceeded by multiple errorC test failures, on the last attempted step.C It is possible that your problemC is ill-posed, and cannot be solvedC using this code. Or, there may be aC discontinuity or a singularity in theC solution. If you are absolutely certainC you want to continue, you should restartC the integration.CC IDID =-10, DDASSL had multiple convergence test failuresC because IRES was equal to minus one.C If you are absolutely certain you wantC to continue, you should restart theC integration.CC IDID =-11, IRES=-2 was encountered, and control is beingC returned to the calling program.CC IDID =-12, DDASSL failed to compute the initial YPRIME.C This could happen because the initialC approximation to YPRIME was not very good, orC if a YPRIME consistent with the initial YC does not exist. The problem could also be causedC by an inaccurate or singular iteration matrix.CC IDID = -13,..,-32 --- Cannot occur with this code.CCC *** Following a terminated task ***CC If IDID= -33, you cannot continue the solution of this problem.C An attempt to do so will result in yourC run being terminated.CCC -------- ERROR MESSAGES ---------------------------------------------CC The SLATEC error print routine XERMSG is called in the event ofC unsuccessful completion of a task. Most of these are treated asC "recoverable errors", which means that (unless the user has directedC otherwise) control will be returned to the calling program forC possible action after the message has been printed.CC In the event of a negative value of IDID other than -33, an appro-C priate message is printed and the "error number" printed by XERMSGC is the value of IDID. There are quite a number of illegal inputC errors that can lead to a returned value IDID=-33. The conditionsC and their printed "error numbers" are as follows:CC Error number ConditionCC 1 Some element of INFO vector is not zero or one.C 2 NEQ .le. 0C 3 MAXORD not in range.C 4 LRW is less than the required length for RWORK.C 5 LIW is less than the required length for IWORK.C 6 Some element of RTOL is .lt. 0C 7 Some element of ATOL is .lt. 0C 8 All elements of RTOL and ATOL are zero.C 9 INFO(4)=1 and TSTOP is behind TOUT.C 10 HMAX .lt. 0.0C 11 TOUT is behind T.C 12 INFO(8)=1 and H0=0.0C 13 Some element of WT is .le. 0.0C 14 TOUT is too close to T to start integration.C 15 INFO(4)=1 and TSTOP is behind T.C 16 --( Not used in this version )--C 17 ML illegal. Either .lt. 0 or .gt. NEQC 18 MU illegal. Either .lt. 0 or .gt. NEQC 19 TOUT = T.CC If DDASSL is called again without any action taken to remove theC cause of an unsuccessful return, XERMSG will be called with a fatalC error flag, which will cause unconditional termination of theC program. There are two such fatal errors:CC Error number -998: The last step was terminated with a negativeC value of IDID other than -33, and no appropriate action wasC taken.CC Error number -999: The previous call was terminated because ofC illegal input (IDID=-33) and there is illegal input in theC present call, as well. (Suspect infinite loop.)CC ---------------------------------------------------------------------CC***REFERENCES A DESCRIPTION OF DASSL: A DIFFERENTIAL/ALGEBRAICC SYSTEM SOLVER, L. R. PETZOLD, SAND82-8637,C SANDIA NATIONAL LABORATORIES, SEPTEMBER 1982.C***ROUTINES CALLED D1MACH, DDAINI, DDANRM, DDASTP, DDATRP, DDAWTS,C XERMSGC***REVISION HISTORY (YYMMDD)C 830315 DATE WRITTENC 880387 Code changes made. All common statements have beenC replaced by a DATA statement, which defines pointers intoC RWORK, and PARAMETER statements which define pointersC into IWORK. As well the documentation has gone throughC grammatical changes.C 881005 The prologue has been changed to mixed case.C The subordinate routines had revision dates changed toC this date, although the documentation for these routinesC is all upper case. No code changes.C 890511 Code changes made. The DATA statement in the declarationC section of DDASSL was replaced with a PARAMETERC statement. Also the statement S = 100.D0 was removedC from the top of the Newton iteration in DDASTP.C The subordinate routines had revision dates changed toC this date.C 890517 The revision date syntax was replaced with the revisionC history syntax. Also the "DECK" comment was added toC the top of all subroutines. These changes are consistentC with new SLATEC guidelines.C The subordinate routines had revision dates changed toC this date. No code changes.C 891013 Code changes made.C Removed all occurrances of FLOAT or DBLE. All operationsC are now performed with "mixed-mode" arithmetic.C Also, specific function names were replaced with genericC function names to be consistent with new SLATEC guidelines.C In particular:C Replaced DSQRT with SQRT everywhere.C Replaced DABS with ABS everywhere.C Replaced DMIN1 with MIN everywhere.C Replaced MIN0 with MIN everywhere.C Replaced DMAX1 with MAX everywhere.C Replaced MAX0 with MAX everywhere.C Replaced DSIGN with SIGN everywhere.C Also replaced REVISION DATE with REVISION HISTORY in allC subordinate routines.C 901004 Miscellaneous changes to prologue to complete conversionC to SLATEC 4.0 format. No code changes. (F.N.Fritsch)C 901009 Corrected GAMS classification code and converted subsidiaryC routines to 4.0 format. No code changes. (F.N.Fritsch)C 901010 Converted XERRWV calls to XERMSG calls. (R.Clemens,AFWL)C 901019 Code changes made.C Merged SLATEC 4.0 changes with previous changes madeC by C. Ulrich. Below is a history of the changes made byC C. Ulrich. (Changes in subsidiary routines are impliedC by this history)C 891228 Bug was found and repaired inside the DDASSLC and DDAINI routines. DDAINI was incorrectlyC returning the initial T with Y and YPRIMEC computed at T+H. The routine now returns T+HC rather than the initial T.C Cosmetic changes made to DDASTP.C 900904 Three modifications were made to fix a bug (insideC DDASSL) re interpolation for continuation calls andC cases where TN is very close to TSTOP:CC 1) In testing for whether H is too large, justC compare H to (TSTOP - TN), rather thanC (TSTOP - TN) * (1-4*UROUND), and set H toC TSTOP - TN. This will force DDASTP to stepC exactly to TSTOP under certain situationsC (i.e. when H returned from DDASTP would otherwiseC take TN beyond TSTOP).CC 2) Inside the DDASTP loop, interpolate exactly toC TSTOP if TN is very close to TSTOP (rather thanC interpolating to within roundoff of TSTOP).CC 3) Modified IDID description for IDID = 2 to say thatC the solution is returned by stepping exactly toC TSTOP, rather than TOUT. (In some cases theC solution is actually obtained by extrapolatingC over a distance near unit roundoff to TSTOP,C but this small distance is deemed acceptable inC these circumstances.)C 901026 Added explicit declarations for all variables and minorC cosmetic changes to prologue, removed unreferenced labels,C and improved XERMSG calls. (FNF)C 901030 Added ERROR MESSAGES section and reworked other sections toC be of more uniform format. (FNF)C 910624 Fixed minor bug related to HMAX (five lines ending inC statement 526 in DDASSL). (LRP)CC***END PROLOGUE DDASSLCC**EndCC Declare arguments.C INTEGER NEQ, INFO(15), IDID, LRW, IWORK(*), LIW, IPAR(*) DOUBLE PRECISION * T, Y(*), YPRIME(*), TOUT, RTOL(*), ATOL(*), RWORK(*), * RPAR(*) EXTERNAL RES, JACCC Declare externals.C EXTERNAL D1MACH, DDAINI, DDANRM, DDASTP, DDATRP, DDAWTS, XERMSG DOUBLE PRECISION D1MACH, DDANRMCC Declare local variables.C INTEGER I, ITEMP, LALPHA, LBETA, LCJ, LCJOLD, LCTF, LDELTA, * LENIW, LENPD, LENRW, LE, LETF, LGAMMA, LH, LHMAX, LHOLD, LIPVT, * LJCALC, LK, LKOLD, LIWM, LML, LMTYPE, LMU, LMXORD, LNJE, LNPD, * LNRE, LNS, LNST, LNSTL, LPD, LPHASE, LPHI, LPSI, LROUND, LS, * LSIGMA, LTN, LTSTOP, LWM, LWT, MBAND, MSAVE, MXORD, NPD, NTEMP, * NZFLG DOUBLE PRECISION * ATOLI, H, HMAX, HMIN, HO, R, RH, RTOLI, TDIST, TN, TNEXT, * TSTOP, UROUND, YPNORM LOGICAL DONEC Auxiliary variables for conversion of values to be included inC error messages. CHARACTER*8 XERN1, XERN2 CHARACTER*16 XERN3, XERN4CC SET POINTERS INTO IWORK PARAMETER (LML=1, LMU=2, LMXORD=3, LMTYPE=4, LNST=11, * LNRE=12, LNJE=13, LETF=14, LCTF=15, LNPD=16, * LIPVT=21, LJCALC=5, LPHASE=6, LK=7, LKOLD=8, * LNS=9, LNSTL=10, LIWM=1)CC SET RELATIVE OFFSET INTO RWORK PARAMETER (NPD=1)CC SET POINTERS INTO RWORK PARAMETER (LTSTOP=1, LHMAX=2, LH=3, LTN=4, * LCJ=5, LCJOLD=6, LHOLD=7, LS=8, LROUND=9, * LALPHA=11, LBETA=17, LGAMMA=23, * LPSI=29, LSIGMA=35, LDELTA=41)CC***FIRST EXECUTABLE STATEMENT DDASSL IF(INFO(1).NE.0)GO TO 100CC-----------------------------------------------------------------------C THIS BLOCK IS EXECUTED FOR THE INITIAL CALL ONLY.C IT CONTAINS CHECKING OF INPUTS AND INITIALIZATIONS.C-----------------------------------------------------------------------CC FIRST CHECK INFO ARRAY TO MAKE SURE ALL ELEMENTS OF INFOC ARE EITHER ZERO OR ONE. DO 10 I=2,11 IF(INFO(I).NE.0.AND.INFO(I).NE.1)GO TO 70110 CONTINUEC IF(NEQ.LE.0)GO TO 702CC CHECK AND COMPUTE MAXIMUM ORDER MXORD=5 IF(INFO(9).EQ.0)GO TO 20 MXORD=IWORK(LMXORD) IF(MXORD.LT.1.OR.MXORD.GT.5)GO TO 70320 IWORK(LMXORD)=MXORDCC COMPUTE MTYPE,LENPD,LENRW.CHECK ML AND MU. IF(INFO(6).NE.0)GO TO 40 LENPD=NEQ**2 LENRW=40+(IWORK(LMXORD)+4)*NEQ+LENPD IF(INFO(5).NE.0)GO TO 30 IWORK(LMTYPE)=2 GO TO 6030 IWORK(LMTYPE)=1 GO TO 6040 IF(IWORK(LML).LT.0.OR.IWORK(LML).GE.NEQ)GO TO 717 IF(IWORK(LMU).LT.0.OR.IWORK(LMU).GE.NEQ)GO TO 718 LENPD=(2*IWORK(LML)+IWORK(LMU)+1)*NEQ IF(INFO(5).NE.0)GO TO 50 IWORK(LMTYPE)=5 MBAND=IWORK(LML)+IWORK(LMU)+1 MSAVE=(NEQ/MBAND)+1 LENRW=40+(IWORK(LMXORD)+4)*NEQ+LENPD+2*MSAVE GO TO 6050 IWORK(LMTYPE)=4 LENRW=40+(IWORK(LMXORD)+4)*NEQ+LENPDCC CHECK LENGTHS OF RWORK AND IWORK60 LENIW=20+NEQ IWORK(LNPD)=LENPD IF(LRW.LT.LENRW)GO TO 704 IF(LIW.LT.LENIW)GO TO 705CC CHECK TO SEE THAT TOUT IS DIFFERENT FROM T IF(TOUT .EQ. T)GO TO 719CC CHECK HMAX IF(INFO(7).EQ.0)GO TO 70 HMAX=RWORK(LHMAX) IF(HMAX.LE.0.0D0)GO TO 71070 CONTINUECC INITIALIZE COUNTERS IWORK(LNST)=0 IWORK(LNRE)=0 IWORK(LNJE)=0C IWORK(LNSTL)=0 IDID=1 GO TO 200CC-----------------------------------------------------------------------C THIS BLOCK IS FOR CONTINUATION CALLSC ONLY. HERE WE CHECK INFO(1),AND IF THEC LAST STEP WAS INTERRUPTED WE CHECK WHETHERC APPROPRIATE ACTION WAS TAKEN.C-----------------------------------------------------------------------C100 CONTINUE IF(INFO(1).EQ.1)GO TO 110 IF(INFO(1).NE.-1)GO TO 701CC IF WE ARE HERE, THE LAST STEP WAS INTERRUPTEDC BY AN ERROR CONDITION FROM DDASTP,ANDC APPROPRIATE ACTION WAS NOT TAKEN. THISC IS A FATAL ERROR. WRITE (XERN1, '(I8) ') IDID CALL XERMSG ('SLATEC', 'DDASSL ', * 'THE LAST STEP TERMINATED WITH A NEGATIVE VALUE OF IDID = ' // * XERN1 // ' AND NO APPROPRIATE ACTION WAS TAKEN. ' // * 'RUN TERMINATED ', -998, 2) RETURN110 CONTINUE IWORK(LNSTL)=IWORK(LNST)CC-----------------------------------------------------------------------C THIS BLOCK IS EXECUTED ON ALL CALLS.C THE ERROR TOLERANCE PARAMETERS AREC CHECKED, AND THE WORK ARRAY POINTERSC ARE SET.C-----------------------------------------------------------------------C200 CONTINUEC CHECK RTOL,ATOL NZFLG=0 RTOLI=RTOL(1) ATOLI=ATOL(1) DO 210 I=1,NEQ IF(INFO(2).EQ.1)RTOLI=RTOL(I) IF(INFO(2).EQ.1)ATOLI=ATOL(I) IF(RTOLI.GT.0.0D0.OR.ATOLI.GT.0.0D0)NZFLG=1 IF(RTOLI.LT.0.0D0)GO TO 706 IF(ATOLI.LT.0.0D0)GO TO 707210 CONTINUE IF(NZFLG.EQ.0)GO TO 708CC SET UP RWORK STORAGE.IWORK STORAGE IS FIXEDC IN DATA STATEMENT. LE=LDELTA+NEQ LWT=LE+NEQ LPHI=LWT+NEQ LPD=LPHI+(IWORK(LMXORD)+1)*NEQ LWM=LPD NTEMP=NPD+IWORK(LNPD) IF(INFO(1).EQ.1)GO TO 400CC-----------------------------------------------------------------------C THIS BLOCK IS EXECUTED ON THE INITIAL CALLC ONLY. SET THE INITIAL STEP SIZE, ANDC THE ERROR WEIGHT VECTOR, AND PHI.C COMPUTE INITIAL YPRIME, IF NECESSARY.C-----------------------------------------------------------------------C TN=T IDID=1CC SET ERROR WEIGHT VECTOR WT CALL DDAWTS(NEQ,INFO(2),RTOL,ATOL,Y,RWORK(LWT),RPAR,IPAR) DO 305 I = 1,NEQ IF(RWORK(LWT+I-1).LE.0.0D0) GO TO 713305 CONTINUECC COMPUTE UNIT ROUNDOFF AND HMIN UROUND = D1MACH(4) RWORK(LROUND) = UROUND HMIN = 4.0D0*UROUND*MAX(ABS(T),ABS(TOUT))CC CHECK INITIAL INTERVAL TO SEE THAT IT IS LONG ENOUGH TDIST = ABS(TOUT - T) IF(TDIST .LT. HMIN) GO TO 714CC CHECK HO, IF THIS WAS INPUT IF (INFO(8) .EQ. 0) GO TO 310 HO = RWORK(LH) IF ((TOUT - T)*HO .LT. 0.0D0) GO TO 711 IF (HO .EQ. 0.0D0) GO TO 712 GO TO 320310 CONTINUECC COMPUTE INITIAL STEPSIZE, TO BE USED BY EITHERC DDASTP OR DDAINI, DEPENDING ON INFO(11) HO = 0.001D0*TDIST YPNORM = DDANRM(NEQ,YPRIME,RWORK(LWT),RPAR,IPAR) IF (YPNORM .GT. 0.5D0/HO) HO = 0.5D0/YPNORM HO = SIGN(HO,TOUT-T)C ADJUST HO IF NECESSARY TO MEET HMAX BOUND320 IF (INFO(7) .EQ. 0) GO TO 330 RH = ABS(HO)/RWORK(LHMAX) IF (RH .GT. 1.0D0) HO = HO/RHC COMPUTE TSTOP, IF APPLICABLE330 IF (INFO(4) .EQ. 0) GO TO 340 TSTOP = RWORK(LTSTOP) IF ((TSTOP - T)*HO .LT. 0.0D0) GO TO 715 IF ((T + HO - TSTOP)*HO .GT. 0.0D0) HO = TSTOP - T IF ((TSTOP - TOUT)*HO .LT. 0.0D0) GO TO 709CC COMPUTE INITIAL DERIVATIVE, UPDATING TN AND Y, IF APPLICABLE340 IF (INFO(11) .EQ. 0) GO TO 350 CALL DDAINI(TN,Y,YPRIME,NEQ, * RES,JAC,HO,RWORK(LWT),IDID,RPAR,IPAR, * RWORK(LPHI),RWORK(LDELTA),RWORK(LE), * RWORK(LWM),IWORK(LIWM),HMIN,RWORK(LROUND), * INFO(10),NTEMP) IF (IDID .LT. 0) GO TO 390CC LOAD H WITH HO. STORE H IN RWORK(LH)350 H = HO RWORK(LH) = HCC LOAD Y AND H*YPRIME INTO PHI(*,1) AND PHI(*,2) ITEMP = LPHI + NEQ DO 370 I = 1,NEQ RWORK(LPHI + I - 1) = Y(I)370 RWORK(ITEMP + I - 1) = H*YPRIME(I)C390 GO TO 500CC-------------------------------------------------------C THIS BLOCK IS FOR CONTINUATION CALLS ONLY. ITSC PURPOSE IS TO CHECK STOP CONDITIONS BEFOREC TAKING A STEP.C ADJUST H IF NECESSARY TO MEET HMAX BOUNDC-------------------------------------------------------C400 CONTINUE UROUND=RWORK(LROUND) DONE = .FALSE. TN=RWORK(LTN) H=RWORK(LH) IF(INFO(7) .EQ. 0) GO TO 410 RH = ABS(H)/RWORK(LHMAX) IF(RH .GT. 1.0D0) H = H/RH410 CONTINUE IF(T .EQ. TOUT) GO TO 719 IF((T - TOUT)*H .GT. 0.0D0) GO TO 711 IF(INFO(4) .EQ. 1) GO TO 430 IF(INFO(3) .EQ. 1) GO TO 420 IF((TN-TOUT)*H.LT.0.0D0)GO TO 490 CALL DDATRP(TN,TOUT,Y,YPRIME,NEQ,IWORK(LKOLD), * RWORK(LPHI),RWORK(LPSI)) T=TOUT IDID = 3 DONE = .TRUE. GO TO 490420 IF((TN-T)*H .LE. 0.0D0) GO TO 490 IF((TN - TOUT)*H .GT. 0.0D0) GO TO 425 CALL DDATRP(TN,TN,Y,YPRIME,NEQ,IWORK(LKOLD), * RWORK(LPHI),RWORK(LPSI)) T = TN IDID = 1 DONE = .TRUE. GO TO 490425 CONTINUE CALL DDATRP(TN,TOUT,Y,YPRIME,NEQ,IWORK(LKOLD), * RWORK(LPHI),RWORK(LPSI)) T = TOUT IDID = 3 DONE = .TRUE. GO TO 490430 IF(INFO(3) .EQ. 1) GO TO 440 TSTOP=RWORK(LTSTOP) IF((TN-TSTOP)*H.GT.0.0D0) GO TO 715 IF((TSTOP-TOUT)*H.LT.0.0D0)GO TO 709 IF((TN-TOUT)*H.LT.0.0D0)GO TO 450 CALL DDATRP(TN,TOUT,Y,YPRIME,NEQ,IWORK(LKOLD), * RWORK(LPHI),RWORK(LPSI)) T=TOUT IDID = 3 DONE = .TRUE. GO TO 490440 TSTOP = RWORK(LTSTOP) IF((TN-TSTOP)*H .GT. 0.0D0) GO TO 715 IF((TSTOP-TOUT)*H .LT. 0.0D0) GO TO 709 IF((TN-T)*H .LE. 0.0D0) GO TO 450 IF((TN - TOUT)*H .GT. 0.0D0) GO TO 445 CALL DDATRP(TN,TN,Y,YPRIME,NEQ,IWORK(LKOLD), * RWORK(LPHI),RWORK(LPSI)) T = TN IDID = 1 DONE = .TRUE. GO TO 490445 CONTINUE CALL DDATRP(TN,TOUT,Y,YPRIME,NEQ,IWORK(LKOLD), * RWORK(LPHI),RWORK(LPSI)) T = TOUT IDID = 3 DONE = .TRUE. GO TO 490450 CONTINUEC CHECK WHETHER WE ARE WITHIN ROUNDOFF OF TSTOP IF(ABS(TN-TSTOP).GT.100.0D0*UROUND* * (ABS(TN)+ABS(H)))GO TO 460 CALL DDATRP(TN,TSTOP,Y,YPRIME,NEQ,IWORK(LKOLD), * RWORK(LPHI),RWORK(LPSI)) IDID=2 T=TSTOP DONE = .TRUE. GO TO 490460 TNEXT=TN+H IF((TNEXT-TSTOP)*H.LE.0.0D0)GO TO 490 H=TSTOP-TN RWORK(LH)=HC490 IF (DONE) GO TO 580CC-------------------------------------------------------C THE NEXT BLOCK CONTAINS THE CALL TO THEC ONE-STEP INTEGRATOR DDASTP.C THIS IS A LOOPING POINT FOR THE INTEGRATION STEPS.C CHECK FOR TOO MANY STEPS.C UPDATE WT.C CHECK FOR TOO MUCH ACCURACY REQUESTED.C COMPUTE MINIMUM STEPSIZE.C-------------------------------------------------------C500 CONTINUEC CHECK FOR FAILURE TO COMPUTE INITIAL YPRIME IF (IDID .EQ. -12) GO TO 527CC CHECK FOR TOO MANY STEPS IF((IWORK(LNST)-IWORK(LNSTL)).LT.500) * GO TO 510 IDID=-1 GO TO 527CC UPDATE WT510 CALL DDAWTS(NEQ,INFO(2),RTOL,ATOL,RWORK(LPHI), * RWORK(LWT),RPAR,IPAR) DO 520 I=1,NEQ IF(RWORK(I+LWT-1).GT.0.0D0)GO TO 520 IDID=-3 GO TO 527520 CONTINUECC TEST FOR TOO MUCH ACCURACY REQUESTED. R=DDANRM(NEQ,RWORK(LPHI),RWORK(LWT),RPAR,IPAR)* * 100.0D0*UROUND IF(R.LE.1.0D0)GO TO 525C MULTIPLY RTOL AND ATOL BY R AND RETURN IF(INFO(2).EQ.1)GO TO 523 RTOL(1)=R*RTOL(1) ATOL(1)=R*ATOL(1) IDID=-2 GO TO 527523 DO 524 I=1,NEQ RTOL(I)=R*RTOL(I)524 ATOL(I)=R*ATOL(I) IDID=-2 GO TO 527525 CONTINUECC COMPUTE MINIMUM STEPSIZE HMIN=4.0D0*UROUND*MAX(ABS(TN),ABS(TOUT))CC TEST H VS. HMAX IF (INFO(7) .EQ. 0) GO TO 526 RH = ABS(H)/RWORK(LHMAX) IF (RH .GT. 1.0D0) H = H/RH526 CONTINUE C CALL DDASTP(TN,Y,YPRIME,NEQ, * RES,JAC,H,RWORK(LWT),INFO(1),IDID,RPAR,IPAR, * RWORK(LPHI),RWORK(LDELTA),RWORK(LE), * RWORK(LWM),IWORK(LIWM), * RWORK(LALPHA),RWORK(LBETA),RWORK(LGAMMA), * RWORK(LPSI),RWORK(LSIGMA), * RWORK(LCJ),RWORK(LCJOLD),RWORK(LHOLD), * RWORK(LS),HMIN,RWORK(LROUND), * IWORK(LPHASE),IWORK(LJCALC),IWORK(LK), * IWORK(LKOLD),IWORK(LNS),INFO(10),NTEMP)527 IF(IDID.LT.0)GO TO 600CC--------------------------------------------------------C THIS BLOCK HANDLES THE CASE OF A SUCCESSFUL RETURNC FROM DDASTP (IDID=1). TEST FOR STOP CONDITIONS.C--------------------------------------------------------C IF(INFO(4).NE.0)GO TO 540 IF(INFO(3).NE.0)GO TO 530 IF((TN-TOUT)*H.LT.0.0D0)GO TO 500 CALL DDATRP(TN,TOUT,Y,YPRIME,NEQ, * IWORK(LKOLD),RWORK(LPHI),RWORK(LPSI)) IDID=3 T=TOUT GO TO 580530 IF((TN-TOUT)*H.GE.0.0D0)GO TO 535 T=TN IDID=1 GO TO 580535 CALL DDATRP(TN,TOUT,Y,YPRIME,NEQ, * IWORK(LKOLD),RWORK(LPHI),RWORK(LPSI)) IDID=3 T=TOUT GO TO 580540 IF(INFO(3).NE.0)GO TO 550 IF((TN-TOUT)*H.LT.0.0D0)GO TO 542 CALL DDATRP(TN,TOUT,Y,YPRIME,NEQ, * IWORK(LKOLD),RWORK(LPHI),RWORK(LPSI)) T=TOUT IDID=3 GO TO 580542 IF(ABS(TN-TSTOP).LE.100.0D0*UROUND* * (ABS(TN)+ABS(H)))GO TO 545 TNEXT=TN+H IF((TNEXT-TSTOP)*H.LE.0.0D0)GO TO 500 H=TSTOP-TN GO TO 500545 CALL DDATRP(TN,TSTOP,Y,YPRIME,NEQ, * IWORK(LKOLD),RWORK(LPHI),RWORK(LPSI)) IDID=2 T=TSTOP GO TO 580550 IF((TN-TOUT)*H.GE.0.0D0)GO TO 555 IF(ABS(TN-TSTOP).LE.100.0D0*UROUND*(ABS(TN)+ABS(H)))GO TO 552 T=TN IDID=1 GO TO 580552 CALL DDATRP(TN,TSTOP,Y,YPRIME,NEQ, * IWORK(LKOLD),RWORK(LPHI),RWORK(LPSI)) IDID=2 T=TSTOP GO TO 580555 CALL DDATRP(TN,TOUT,Y,YPRIME,NEQ, * IWORK(LKOLD),RWORK(LPHI),RWORK(LPSI)) T=TOUT IDID=3 GO TO 580CC--------------------------------------------------------C ALL SUCCESSFUL RETURNS FROM DDASSL ARE MADE FROMC THIS BLOCK.C--------------------------------------------------------C580 CONTINUE RWORK(LTN)=TN RWORK(LH)=H RETURNCC-----------------------------------------------------------------------C THIS BLOCK HANDLES ALL UNSUCCESSFULC RETURNS OTHER THAN FOR ILLEGAL INPUT.C-----------------------------------------------------------------------C600 CONTINUE ITEMP=-IDID GO TO (610,620,630,690,690,640,650,660,670,675, * 680,685), ITEMPCC THE MAXIMUM NUMBER OF STEPS WAS TAKEN BEFOREC REACHING TOUT610 WRITE (XERN3, '(1P,D15.6) ') TN CALL XERMSG ('SLATEC', 'DDASSL ', * 'AT CURRENT T = ' // XERN3 // ' 500 STEPS TAKEN ON THIS ' // * 'CALL BEFORE REACHING TOUT ', IDID, 1) GO TO 690CC TOO MUCH ACCURACY FOR MACHINE PRECISION620 WRITE (XERN3, '(1P,D15.6) ') TN CALL XERMSG ('SLATEC', 'DDASSL ', * 'AT T = ' // XERN3 // ' TOO MUCH ACCURACY REQUESTED FOR ' // * 'PRECISION OF MACHINE. RTOL AND ATOL WERE INCREASED TO ' // * 'APPROPRIATE VALUES ', IDID, 1) GO TO 690CC WT(I) .LE. 0.0 FOR SOME I (NOT AT START OF PROBLEM)630 WRITE (XERN3, '(1P,D15.6) ') TN CALL XERMSG ('SLATEC', 'DDASSL ', * 'AT T = ' // XERN3 // ' SOME ELEMENT OF WT HAS BECOME .LE. ' // * '0.0 ', IDID, 1) GO TO 690CC ERROR TEST FAILED REPEATEDLY OR WITH H=HMIN640 WRITE (XERN3, '(1P,D15.6) ') TN WRITE (XERN4, '(1P,D15.6) ') H CALL XERMSG ('SLATEC', 'DDASSL ', * 'AT T = ' // XERN3 // ' AND STEPSIZE H = ' // XERN4 // * ' THE ERROR TEST FAILED REPEATEDLY OR WITH ABS(H)=HMIN ', * IDID, 1) GO TO 690CC CORRECTOR CONVERGENCE FAILED REPEATEDLY OR WITH H=HMIN650 WRITE (XERN3, '(1P,D15.6) ') TN WRITE (XERN4, '(1P,D15.6) ') H CALL XERMSG ('SLATEC', 'DDASSL ', * 'AT T = ' // XERN3 // ' AND STEPSIZE H = ' // XERN4 // * ' THE CORRECTOR FAILED TO CONVERGE REPEATEDLY OR WITH ' // * 'ABS(H)=HMIN ', IDID, 1) GO TO 690CC THE ITERATION MATRIX IS SINGULAR660 WRITE (XERN3, '(1P,D15.6) ') TN WRITE (XERN4, '(1P,D15.6) ') H CALL XERMSG ('SLATEC', 'DDASSL ', * 'AT T = ' // XERN3 // ' AND STEPSIZE H = ' // XERN4 // * ' THE ITERATION MATRIX IS SINGULAR ', IDID, 1) GO TO 690CC CORRECTOR FAILURE PRECEEDED BY ERROR TEST FAILURES.670 WRITE (XERN3, '(1P,D15.6) ') TN WRITE (XERN4, '(1P,D15.6) ') H CALL XERMSG ('SLATEC', 'DDASSL ', * 'AT T = ' // XERN3 // ' AND STEPSIZE H = ' // XERN4 // * ' THE CORRECTOR COULD NOT CONVERGE. ALSO, THE ERROR TEST ' // * 'FAILED REPEATEDLY. ', IDID, 1) GO TO 690CC CORRECTOR FAILURE BECAUSE IRES = -1675 WRITE (XERN3, '(1P,D15.6) ') TN WRITE (XERN4, '(1P,D15.6) ') H CALL XERMSG ('SLATEC', 'DDASSL ', * 'AT T = ' // XERN3 // ' AND STEPSIZE H = ' // XERN4 // * ' THE CORRECTOR COULD NOT CONVERGE BECAUSE IRES WAS EQUAL ' // * 'TO MINUS ONE ', IDID, 1) GO TO 690CC FAILURE BECAUSE IRES = -2680 WRITE (XERN3, '(1P,D15.6) ') TN WRITE (XERN4, '(1P,D15.6) ') H CALL XERMSG ('SLATEC', 'DDASSL ', * 'AT T = ' // XERN3 // ' AND STEPSIZE H = ' // XERN4 // * ' IRES WAS EQUAL TO MINUS TWO ', IDID, 1) GO TO 690CC FAILED TO COMPUTE INITIAL YPRIME685 WRITE (XERN3, '(1P,D15.6) ') TN WRITE (XERN4, '(1P,D15.6) ') HO CALL XERMSG ('SLATEC', 'DDASSL ', * 'AT T = ' // XERN3 // ' AND STEPSIZE H = ' // XERN4 // * ' THE INITIAL YPRIME COULD NOT BE COMPUTED ', IDID, 1) GO TO 690C690 CONTINUE INFO(1)=-1 T=TN RWORK(LTN)=TN RWORK(LH)=H RETURNCC-----------------------------------------------------------------------C THIS BLOCK HANDLES ALL ERROR RETURNS DUEC TO ILLEGAL INPUT, AS DETECTED BEFORE CALLINGC DDASTP. FIRST THE ERROR MESSAGE ROUTINE ISC CALLED. IF THIS HAPPENS TWICE INC SUCCESSION, EXECUTION IS TERMINATEDCC-----------------------------------------------------------------------701 CALL XERMSG ('SLATEC', 'DDASSL ', * 'SOME ELEMENT OF INFO VECTOR IS NOT ZERO OR ONE ', 1, 1) GO TO 750C702 WRITE (XERN1, '(I8) ') NEQ CALL XERMSG ('SLATEC', 'DDASSL ', * 'NEQ = ' // XERN1 // ' .LE. 0 ', 2, 1) GO TO 750C703 WRITE (XERN1, '(I8) ') MXORD CALL XERMSG ('SLATEC', 'DDASSL ', * 'MAXORD = ' // XERN1 // ' NOT IN RANGE ', 3, 1) GO TO 750C704 WRITE (XERN1, '(I8) ') LENRW WRITE (XERN2, '(I8) ') LRW CALL XERMSG ('SLATEC', 'DDASSL ', * 'RWORK LENGTH NEEDED, LENRW = ' // XERN1 // * ', EXCEEDS LRW = ' // XERN2, 4, 1) GO TO 750C705 WRITE (XERN1, '(I8) ') LENIW WRITE (XERN2, '(I8) ') LIW CALL XERMSG ('SLATEC', 'DDASSL ', * 'IWORK LENGTH NEEDED, LENIW = ' // XERN1 // * ', EXCEEDS LIW = ' // XERN2, 5, 1) GO TO 750C706 CALL XERMSG ('SLATEC', 'DDASSL ', * 'SOME ELEMENT OF RTOL IS .LT. 0 ', 6, 1) GO TO 750C707 CALL XERMSG ('SLATEC', 'DDASSL ', * 'SOME ELEMENT OF ATOL IS .LT. 0 ', 7, 1) GO TO 750C708 CALL XERMSG ('SLATEC', 'DDASSL ', * 'ALL ELEMENTS OF RTOL AND ATOL ARE ZERO ', 8, 1) GO TO 750C709 WRITE (XERN3, '(1P,D15.6) ') TSTOP WRITE (XERN4, '(1P,D15.6) ') TOUT CALL XERMSG ('SLATEC', 'DDASSL ', * 'INFO(4) = 1 AND TSTOP = ' // XERN3 // ' BEHIND TOUT = ' // * XERN4, 9, 1) GO TO 750C710 WRITE (XERN3, '(1P,D15.6) ') HMAX CALL XERMSG ('SLATEC', 'DDASSL ', * 'HMAX = ' // XERN3 // ' .LT. 0.0 ', 10, 1) GO TO 750C711 WRITE (XERN3, '(1P,D15.6) ') TOUT WRITE (XERN4, '(1P,D15.6) ') T CALL XERMSG ('SLATEC', 'DDASSL ', * 'TOUT = ' // XERN3 // ' BEHIND T = ' // XERN4, 11, 1) GO TO 750C712 CALL XERMSG ('SLATEC', 'DDASSL ', * 'INFO(8)=1 AND H0=0.0 ', 12, 1) GO TO 750C713 CALL XERMSG ('SLATEC', 'DDASSL ', * 'SOME ELEMENT OF WT IS .LE. 0.0 ', 13, 1) GO TO 750C714 WRITE (XERN3, '(1P,D15.6) ') TOUT WRITE (XERN4, '(1P,D15.6) ') T CALL XERMSG ('SLATEC', 'DDASSL ', * 'TOUT = ' // XERN3 // ' TOO CLOSE TO T = ' // XERN4 // * ' TO START INTEGRATION ', 14, 1) GO TO 750C715 WRITE (XERN3, '(1P,D15.6) ') TSTOP WRITE (XERN4, '(1P,D15.6) ') T CALL XERMSG ('SLATEC', 'DDASSL ', * 'INFO(4)=1 AND TSTOP = ' // XERN3 // ' BEHIND T = ' // XERN4, * 15, 1) GO TO 750C717 WRITE (XERN1, '(I8) ') IWORK(LML) CALL XERMSG ('SLATEC', 'DDASSL ', * 'ML = ' // XERN1 // ' ILLEGAL. EITHER .LT. 0 OR .GT. NEQ ', * 17, 1) GO TO 750C718 WRITE (XERN1, '(I8) ') IWORK(LMU) CALL XERMSG ('SLATEC', 'DDASSL ', * 'MU = ' // XERN1 // ' ILLEGAL. EITHER .LT. 0 OR .GT. NEQ ', * 18, 1) GO TO 750C719 WRITE (XERN3, '(1P,D15.6) ') TOUT CALL XERMSG ('SLATEC', 'DDASSL ', * 'TOUT = T = ' // XERN3, 19, 1) GO TO 750C750 IDID=-33 IF(INFO(1).EQ.-1) THEN CALL XERMSG ('SLATEC', 'DDASSL ', * 'REPEATED OCCURRENCES OF ILLEGAL INPUT$$ ' // * 'RUN TERMINATED. APPARENT INFINITE LOOP

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