*DECK SNSQ SUBROUTINE SNSQ (FCN, JAC, IOPT, N, X, FVEC, FJAC, LDFJAC, XTOL, + MAXFEV, ML, MU, EPSFCN, DIAG, MODE, FACTOR, NPRINT, INFO, NFEV, + NJEV, R, LR, QTF, WA1, WA2, WA3, WA4) C***BEGIN PROLOGUE SNSQ C***PURPOSE Find a zero of a system of a N nonlinear functions in N C variables by a modification of the Powell hybrid method. C***LIBRARY SLATEC C***CATEGORY F2A C***TYPE SINGLE PRECISION (SNSQ-S, DNSQ-D) C***KEYWORDS NONLINEAR SQUARE SYSTEM, POWELL HYBRID METHOD, ZEROS C***AUTHOR Hiebert, K. L., (SNLA) C***DESCRIPTION C C 1. Purpose. C C The purpose of SNSQ is to find a zero of a system of N non- C linear functions in N variables by a modification of the Powell C hybrid method. The user must provide a subroutine which calcu- C lates the functions. The user has the option of either to C provide a subroutine which calculates the Jacobian or to let the C code calculate it by a forward-difference approximation. C This code is the combination of the MINPACK codes (Argonne) C HYBRD and HYBRDJ. C C C 2. Subroutine and Type Statements. C C SUBROUTINE SNSQ(FCN,JAC,IOPT,N,X,FVEC,FJAC,LDFJAC,XTOL,MAXFEV, C * ML,MU,EPSFCN,DIAG,MODE,FACTOR,NPRINT,INFO,NFEV, C * NJEV,R,LR,QTF,WA1,WA2,WA3,WA4) C INTEGER IOPT,N,MAXFEV,ML,MU,MODE,NPRINT,INFO,NFEV,LDFJAC,NJEV,LR C REAL XTOL,EPSFCN,FACTOR C REAL X(N),FVEC(N),DIAG(N),FJAC(LDFJAC,N),R(LR),QTF(N), C * WA1(N),WA2(N),WA3(N),WA4(N) C EXTERNAL FCN,JAC C C C 3. Parameters. C C Parameters designated as input parameters must be specified on C entry to SNSQ and are not changed on exit, while parameters C designated as output parameters need not be specified on entry C and are set to appropriate values on exit from SNSQ. C C FCN is the name of the user-supplied subroutine which calculates C the functions. FCN must be declared in an EXTERNAL statement C in the user calling program, and should be written as follows. C C SUBROUTINE FCN(N,X,FVEC,IFLAG) C INTEGER N,IFLAG C REAL X(N),FVEC(N) C ---------- C Calculate the functions at X and C return this vector in FVEC. C ---------- C RETURN C END C C The value of IFLAG should not be changed by FCN unless the C user wants to terminate execution of SNSQ. In this case, set C IFLAG to a negative integer. C C JAC is the name of the user-supplied subroutine which calculates C the Jacobian. If IOPT=1, then JAC must be declared in an C EXTERNAL statement in the user calling program, and should be C written as follows. C C SUBROUTINE JAC(N,X,FVEC,FJAC,LDFJAC,IFLAG) C INTEGER N,LDFJAC,IFLAG C REAL X(N),FVEC(N),FJAC(LDFJAC,N) C ---------- C Calculate the Jacobian at X and return this C matrix in FJAC. FVEC contains the function C values at X and should not be altered. C ---------- C RETURN C END C C The value of IFLAG should not be changed by JAC unless the C user wants to terminate execution of SNSQ. In this case, set C IFLAG to a negative integer. C C If IOPT=2, JAC can be ignored (treat it as a dummy argument). C C IOPT is an input variable which specifies how the Jacobian will C be calculated. If IOPT=1, then the user must supply the C Jacobian through the subroutine JAC. If IOPT=2, then the C code will approximate the Jacobian by forward-differencing. C C N is a positive integer input variable set to the number of C functions and variables. C C X is an array of length N. On input, X must contain an initial C estimate of the solution vector. On output, X contains the C final estimate of the solution vector. C C FVEC is an output array of length N which contains the functions C evaluated at the output X. C C FJAC is an output N by N array which contains the orthogonal C matrix Q produced by the QR factorization of the final approx- C imate Jacobian. C C LDFJAC is a positive integer input variable not less than N C which specifies the leading dimension of the array FJAC. C C XTOL is a non-negative input variable. Termination occurs when C the relative error between two consecutive iterates is at most C XTOL. Therefore, XTOL measures the relative error desired in C the approximate solution. Section 4 contains more details C about XTOL. C C MAXFEV is a positive integer input variable. Termination occurs C when the number of calls to FCN is at least MAXFEV by the end C of an iteration. C C ML is a non-negative integer input variable which specifies the C number of subdiagonals within the band of the Jacobian matrix. C If the Jacobian is not banded or IOPT=1, set ML to at C least N - 1. C C MU is a non-negative integer input variable which specifies the C number of superdiagonals within the band of the Jacobian C matrix. If the Jacobian is not banded or IOPT=1, set MU to at C least N - 1. C C EPSFCN is an input variable used in determining a suitable step C for the forward-difference approximation. This approximation C assumes that the relative errors in the functions are of the C order of EPSFCN. If EPSFCN is less than the machine preci- C sion, it is assumed that the relative errors in the functions C are of the order of the machine precision. If IOPT=1, then C EPSFCN can be ignored (treat it as a dummy argument). C C DIAG is an array of length N. If MODE = 1 (see below), DIAG is C internally set. If MODE = 2, DIAG must contain positive C entries that serve as implicit (multiplicative) scale factors C for the variables. C C MODE is an integer input variable. If MODE = 1, the variables C will be scaled internally. If MODE = 2, the scaling is speci- C fied by the input DIAG. Other values of MODE are equivalent C to MODE = 1. C C FACTOR is a positive input variable used in determining the ini- C tial step bound. This bound is set to the product of FACTOR C and the Euclidean norm of DIAG*X if nonzero, or else to FACTOR C itself. In most cases FACTOR should lie in the interval C (.1,100.). 100. is a generally recommended value. C C NPRINT is an integer input variable that enables controlled C printing of iterates if it is positive. In this case, FCN is C called with IFLAG = 0 at the beginning of the first iteration C and every NPRINT iteration thereafter and immediately prior C to return, with X and FVEC available for printing. Appropriate C print statements must be added to FCN(see example). If NPRINT C is not positive, no special calls of FCN with IFLAG = 0 are C made. C C INFO is an integer output variable. If the user has terminated C execution, INFO is set to the (negative) value of IFLAG. See C description of FCN and JAC. Otherwise, INFO is set as follows. C C INFO = 0 improper input parameters. C C INFO = 1 relative error between two consecutive iterates is C at most XTOL. C C INFO = 2 number of calls to FCN has reached or exceeded C MAXFEV. C C INFO = 3 XTOL is too small. No further improvement in the C approximate solution X is possible. C C INFO = 4 iteration is not making good progress, as measured C by the improvement from the last five Jacobian eval- C uations. C C INFO = 5 iteration is not making good progress, as measured C by the improvement from the last ten iterations. C C Sections 4 and 5 contain more details about INFO. C C NFEV is an integer output variable set to the number of calls to C FCN. C C NJEV is an integer output variable set to the number of calls to C JAC. (If IOPT=2, then NJEV is set to zero.) C C R is an output array of length LR which contains the upper C triangular matrix produced by the QR factorization of the C final approximate Jacobian, stored rowwise. C C LR is a positive integer input variable not less than C (N*(N+1))/2. C C QTF is an output array of length N which contains the vector C (Q TRANSPOSE)*FVEC. C C WA1, WA2, WA3, and WA4 are work arrays of length N. C C C 4. Successful Completion. C C The accuracy of SNSQ is controlled by the convergence parameter C XTOL. This parameter is used in a test which makes a comparison C between the approximation X and a solution XSOL. SNSQ termi- C nates when the test is satisfied. If the convergence parameter C is less than the machine precision (as defined by the function C R1MACH(4)), then SNSQ only attempts to satisfy the test C defined by the machine precision. Further progress is not C usually possible. C C The test assumes that the functions are reasonably well behaved, C and, if the Jacobian is supplied by the user, that the functions C and the Jacobian are coded consistently. If these conditions C are not satisfied, then SNSQ may incorrectly indicate conver- C gence. The coding of the Jacobian can be checked by the C subroutine CHKDER. If the Jacobian is coded correctly or IOPT=2, C then the validity of the answer can be checked, for example, by C rerunning SNSQ with a tighter tolerance. C C Convergence Test. If ENORM(Z) denotes the Euclidean norm of a C vector Z and D is the diagonal matrix whose entries are C defined by the array DIAG, then this test attempts to guaran- C tee that C C ENORM(D*(X-XSOL)) .LE. XTOL*ENORM(D*XSOL). C C If this condition is satisfied with XTOL = 10**(-K), then the C larger components of D*X have K significant decimal digits and C INFO is set to 1. There is a danger that the smaller compo- C nents of D*X may have large relative errors, but the fast rate C of convergence of SNSQ usually avoids this possibility. C Unless high precision solutions are required, the recommended C value for XTOL is the square root of the machine precision. C C C 5. Unsuccessful Completion. C C Unsuccessful termination of SNSQ can be due to improper input C parameters, arithmetic interrupts, an excessive number of func- C tion evaluations, or lack of good progress. C C Improper Input Parameters. INFO is set to 0 if IOPT .LT. 1, C or IOPT .GT. 2, or N .LE. 0, or LDFJAC .LT. N, or C XTOL .LT. 0.E0, or MAXFEV .LE. 0, or ML .LT. 0, or MU .LT. 0, C or FACTOR .LE. 0.E0, or LR .LT. (N*(N+1))/2. C C Arithmetic Interrupts. If these interrupts occur in the FCN C subroutine during an early stage of the computation, they may C be caused by an unacceptable choice of X by SNSQ. In this C case, it may be possible to remedy the situation by rerunning C SNSQ with a smaller value of FACTOR. C C Excessive Number of Function Evaluations. A reasonable value C for MAXFEV is 100*(N+1) for IOPT=1 and 200*(N+1) for IOPT=2. C If the number of calls to FCN reaches MAXFEV, then this C indicates that the routine is converging very slowly as C measured by the progress of FVEC, and INFO is set to 2. This C situation should be unusual because, as indicated below, lack C of good progress is usually diagnosed earlier by SNSQ, C causing termination with INFO = 4 or INFO = 5. C C Lack of Good Progress. SNSQ searches for a zero of the system C by minimizing the sum of the squares of the functions. In so C doing, it can become trapped in a region where the minimum C does not correspond to a zero of the system and, in this situ- C ation, the iteration eventually fails to make good progress. C In particular, this will happen if the system does not have a C zero. If the system has a zero, rerunning SNSQ from a dif- C ferent starting point may be helpful. C C C 6. Characteristics of the Algorithm. C C SNSQ is a modification of the Powell hybrid method. Two of its C main characteristics involve the choice of the correction as a C convex combination of the Newton and scaled gradient directions, C and the updating of the Jacobian by the rank-1 method of Broy- C den. The choice of the correction guarantees (under reasonable C conditions) global convergence for starting points far from the C solution and a fast rate of convergence. The Jacobian is C calculated at the starting point by either the user-supplied C subroutine or a forward-difference approximation, but it is not C recalculated until the rank-1 method fails to produce satis- C factory progress. C C Timing. The time required by SNSQ to solve a given problem C depends on N, the behavior of the functions, the accuracy C requested, and the starting point. The number of arithmetic C operations needed by SNSQ is about 11.5*(N**2) to process C each evaluation of the functions (call to FCN) and 1.3*(N**3) C to process each evaluation of the Jacobian (call to JAC, C if IOPT = 1). Unless FCN and JAC can be evaluated quickly, C the timing of SNSQ will be strongly influenced by the time C spent in FCN and JAC. C C Storage. SNSQ requires (3*N**2 + 17*N)/2 single precision C storage locations, in addition to the storage required by the C program. There are no internally declared storage arrays. C C C 7. Example. C C The problem is to determine the values of X(1), X(2), ..., X(9), C which solve the system of tridiagonal equations C C (3-2*X(1))*X(1) -2*X(2) = -1 C -X(I-1) + (3-2*X(I))*X(I) -2*X(I+1) = -1, I=2-8 C -X(8) + (3-2*X(9))*X(9) = -1 C C ********** C C PROGRAM TEST C C C C Driver for SNSQ example. C C C INTEGER J,IOPT,N,MAXFEV,ML,MU,MODE,NPRINT,INFO,NFEV,LDFJAC,LR, C * NWRITE C REAL XTOL,EPSFCN,FACTOR,FNORM C REAL X(9),FVEC(9),DIAG(9),FJAC(9,9),R(45),QTF(9), C * WA1(9),WA2(9),WA3(9),WA4(9) C REAL ENORM,R1MACH C EXTERNAL FCN C DATA NWRITE /6/ C C C IOPT = 2 C N = 9 C C C C The following starting values provide a rough solution. C C C DO 10 J = 1, 9 C X(J) = -1.E0 C 10 CONTINUE C C C LDFJAC = 9 C LR = 45 C C C C Set XTOL to the square root of the machine precision. C C Unless high precision solutions are required, C C this is the recommended setting. C C C XTOL = SQRT(R1MACH(4)) C C C MAXFEV = 2000 C ML = 1 C MU = 1 C EPSFCN = 0.E0 C MODE = 2 C DO 20 J = 1, 9 C DIAG(J) = 1.E0 C 20 CONTINUE C FACTOR = 1.E2 C NPRINT = 0 C C C CALL SNSQ(FCN,JAC,IOPT,N,X,FVEC,FJAC,LDFJAC,XTOL,MAXFEV,ML,MU, C * EPSFCN,DIAG,MODE,FACTOR,NPRINT,INFO,NFEV,NJEV, C * R,LR,QTF,WA1,WA2,WA3,WA4) C FNORM = ENORM(N,FVEC) C WRITE (NWRITE,1000) FNORM,NFEV,INFO,(X(J),J=1,N) C STOP C 1000 FORMAT (5X,' FINAL L2 NORM OF THE RESIDUALS',E15.7 // C * 5X,' NUMBER OF FUNCTION EVALUATIONS',I10 // C * 5X,' EXIT PARAMETER',16X,I10 // C * 5X,' FINAL APPROXIMATE SOLUTION' // (5X,3E15.7)) C END C SUBROUTINE FCN(N,X,FVEC,IFLAG) C INTEGER N,IFLAG C REAL X(N),FVEC(N) C INTEGER K C REAL ONE,TEMP,TEMP1,TEMP2,THREE,TWO,ZERO C DATA ZERO,ONE,TWO,THREE /0.E0,1.E0,2.E0,3.E0/ C C C IF (IFLAG .NE. 0) GO TO 5 C C C C Insert print statements here when NPRINT is positive. C C C RETURN C 5 CONTINUE C DO 10 K = 1, N C TEMP = (THREE - TWO*X(K))*X(K) C TEMP1 = ZERO C IF (K .NE. 1) TEMP1 = X(K-1) C TEMP2 = ZERO C IF (K .NE. N) TEMP2 = X(K+1) C FVEC(K) = TEMP - TEMP1 - TWO*TEMP2 + ONE C 10 CONTINUE C RETURN C END C C Results obtained with different compilers or machines C may be slightly different. C C FINAL L2 NORM OF THE RESIDUALS 0.1192636E-07 C C NUMBER OF FUNCTION EVALUATIONS 14 C C EXIT PARAMETER 1 C C FINAL APPROXIMATE SOLUTION C C -0.5706545E+00 -0.6816283E+00 -0.7017325E+00 C -0.7042129E+00 -0.7013690E+00 -0.6918656E+00 C -0.6657920E+00 -0.5960342E+00 -0.4164121E+00 C C***REFERENCES M. J. D. Powell, A hybrid method for nonlinear equa- C tions. In Numerical Methods for Nonlinear Algebraic C Equations, P. Rabinowitz, Editor. Gordon and Breach, C 1988. C***ROUTINES CALLED DOGLEG, ENORM, FDJAC1, QFORM, QRFAC, R1MACH, C R1MPYQ, R1UPDT, XERMSG C***REVISION HISTORY (YYMMDD) C 800301 DATE WRITTEN C 890531 Changed all specific intrinsics to generic. (WRB) C 890831 Modified array declarations. (WRB) C 890831 REVISION DATE from Version 3.2 C 891214 Prologue converted to Version 4.0 format. (BAB) C 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ) C 920501 Reformatted the REFERENCES section. (WRB) C***END PROLOGUE SNSQ INTEGER IOPT,N,MAXFEV,ML,MU,MODE,NPRINT,INFO,NFEV,LDFJAC,LR,NJEV REAL XTOL,EPSFCN,FACTOR REAL X(*),FVEC(*),DIAG(*),FJAC(LDFJAC,*),R(LR),QTF(*),WA1(*), 1 WA2(*),WA3(*),WA4(*) EXTERNAL FCN INTEGER I,IFLAG,ITER,J,JM1,L,NCFAIL,NCSUC,NSLOW1,NSLOW2 INTEGER IWA(1) LOGICAL JEVAL,SING REAL ACTRED,DELTA,EPSMCH,FNORM,FNORM1,ONE,PNORM,PRERED,P1,P5, 1 P001,P0001,RATIO,SUM,TEMP,XNORM,ZERO REAL R1MACH,ENORM SAVE ONE, P1, P5, P001, P0001, ZERO DATA ONE,P1,P5,P001,P0001,ZERO 1 /1.0E0,1.0E-1,5.0E-1,1.0E-3,1.0E-4,0.0E0/ C C***FIRST EXECUTABLE STATEMENT SNSQ EPSMCH = R1MACH(4) C INFO = 0 IFLAG = 0 NFEV = 0 NJEV = 0 C C CHECK THE INPUT PARAMETERS FOR ERRORS. C IF (IOPT .LT. 1 .OR. IOPT .GT. 2 .OR. 1 N .LE. 0 .OR. XTOL .LT. ZERO .OR. MAXFEV .LE. 0 2 .OR. ML .LT. 0 .OR. MU .LT. 0 .OR. FACTOR .LE. ZERO 3 .OR. LDFJAC .LT. N .OR. LR .LT. (N*(N + 1))/2) GO TO 300 IF (MODE .NE. 2) GO TO 20 DO 10 J = 1, N IF (DIAG(J) .LE. ZERO) GO TO 300 10 CONTINUE 20 CONTINUE C C EVALUATE THE FUNCTION AT THE STARTING POINT C AND CALCULATE ITS NORM. C IFLAG = 1 CALL FCN(N,X,FVEC,IFLAG) NFEV = 1 IF (IFLAG .LT. 0) GO TO 300 FNORM = ENORM(N,FVEC) C C INITIALIZE ITERATION COUNTER AND MONITORS. C ITER = 1 NCSUC = 0 NCFAIL = 0 NSLOW1 = 0 NSLOW2 = 0 C C BEGINNING OF THE OUTER LOOP. C 30 CONTINUE JEVAL = .TRUE. C C CALCULATE THE JACOBIAN MATRIX. C IF (IOPT .EQ. 2) GO TO 31 C C USER SUPPLIES JACOBIAN C CALL JAC(N,X,FVEC,FJAC,LDFJAC,IFLAG) NJEV = NJEV+1 GO TO 32 C C CODE APPROXIMATES THE JACOBIAN C 31 IFLAG = 2 CALL FDJAC1(FCN,N,X,FVEC,FJAC,LDFJAC,IFLAG,ML,MU,EPSFCN,WA1, 1 WA2) NFEV = NFEV + MIN(ML+MU+1,N) C 32 IF (IFLAG .LT. 0) GO TO 300 C C COMPUTE THE QR FACTORIZATION OF THE JACOBIAN. C CALL QRFAC(N,N,FJAC,LDFJAC,.FALSE.,IWA,1,WA1,WA2,WA3) C C ON THE FIRST ITERATION AND IF MODE IS 1, SCALE ACCORDING C TO THE NORMS OF THE COLUMNS OF THE INITIAL JACOBIAN. C IF (ITER .NE. 1) GO TO 70 IF (MODE .EQ. 2) GO TO 50 DO 40 J = 1, N DIAG(J) = WA2(J) IF (WA2(J) .EQ. ZERO) DIAG(J) = ONE 40 CONTINUE 50 CONTINUE C C ON THE FIRST ITERATION, CALCULATE THE NORM OF THE SCALED X C AND INITIALIZE THE STEP BOUND DELTA. C DO 60 J = 1, N WA3(J) = DIAG(J)*X(J) 60 CONTINUE XNORM = ENORM(N,WA3) DELTA = FACTOR*XNORM IF (DELTA .EQ. ZERO) DELTA = FACTOR 70 CONTINUE C C FORM (Q TRANSPOSE)*FVEC AND STORE IN QTF. C DO 80 I = 1, N QTF(I) = FVEC(I) 80 CONTINUE DO 120 J = 1, N IF (FJAC(J,J) .EQ. ZERO) GO TO 110 SUM = ZERO DO 90 I = J, N SUM = SUM + FJAC(I,J)*QTF(I) 90 CONTINUE TEMP = -SUM/FJAC(J,J) DO 100 I = J, N QTF(I) = QTF(I) + FJAC(I,J)*TEMP 100 CONTINUE 110 CONTINUE 120 CONTINUE C C COPY THE TRIANGULAR FACTOR OF THE QR FACTORIZATION INTO R. C SING = .FALSE. DO 150 J = 1, N L = J JM1 = J - 1 IF (JM1 .LT. 1) GO TO 140 DO 130 I = 1, JM1 R(L) = FJAC(I,J) L = L + N - I 130 CONTINUE 140 CONTINUE R(L) = WA1(J) IF (WA1(J) .EQ. ZERO) SING = .TRUE. 150 CONTINUE C C ACCUMULATE THE ORTHOGONAL FACTOR IN FJAC. C CALL QFORM(N,N,FJAC,LDFJAC,WA1) C C RESCALE IF NECESSARY. C IF (MODE .EQ. 2) GO TO 170 DO 160 J = 1, N DIAG(J) = MAX(DIAG(J),WA2(J)) 160 CONTINUE 170 CONTINUE C C BEGINNING OF THE INNER LOOP. C 180 CONTINUE C C IF REQUESTED, CALL FCN TO ENABLE PRINTING OF ITERATES. C IF (NPRINT .LE. 0) GO TO 190 IFLAG = 0 IF (MOD(ITER-1,NPRINT) .EQ. 0) CALL FCN(N,X,FVEC,IFLAG) IF (IFLAG .LT. 0) GO TO 300 190 CONTINUE C C DETERMINE THE DIRECTION P. C CALL DOGLEG(N,R,LR,DIAG,QTF,DELTA,WA1,WA2,WA3) C C STORE THE DIRECTION P AND X + P. CALCULATE THE NORM OF P. C DO 200 J = 1, N WA1(J) = -WA1(J) WA2(J) = X(J) + WA1(J) WA3(J) = DIAG(J)*WA1(J) 200 CONTINUE PNORM = ENORM(N,WA3) C C ON THE FIRST ITERATION, ADJUST THE INITIAL STEP BOUND. C IF (ITER .EQ. 1) DELTA = MIN(DELTA,PNORM) C C EVALUATE THE FUNCTION AT X + P AND CALCULATE ITS NORM. C IFLAG = 1 CALL FCN(N,WA2,WA4,IFLAG) NFEV = NFEV + 1 IF (IFLAG .LT. 0) GO TO 300 FNORM1 = ENORM(N,WA4) C C COMPUTE THE SCALED ACTUAL REDUCTION. C ACTRED = -ONE IF (FNORM1 .LT. FNORM) ACTRED = ONE - (FNORM1/FNORM)**2 C C COMPUTE THE SCALED PREDICTED REDUCTION. C L = 1 DO 220 I = 1, N SUM = ZERO DO 210 J = I, N SUM = SUM + R(L)*WA1(J) L = L + 1 210 CONTINUE WA3(I) = QTF(I) + SUM 220 CONTINUE TEMP = ENORM(N,WA3) PRERED = ZERO IF (TEMP .LT. FNORM) PRERED = ONE - (TEMP/FNORM)**2 C C COMPUTE THE RATIO OF THE ACTUAL TO THE PREDICTED C REDUCTION. C RATIO = ZERO IF (PRERED .GT. ZERO) RATIO = ACTRED/PRERED C C UPDATE THE STEP BOUND. C IF (RATIO .GE. P1) GO TO 230 NCSUC = 0 NCFAIL = NCFAIL + 1 DELTA = P5*DELTA GO TO 240 230 CONTINUE NCFAIL = 0 NCSUC = NCSUC + 1 IF (RATIO .GE. P5 .OR. NCSUC .GT. 1) 1 DELTA = MAX(DELTA,PNORM/P5) IF (ABS(RATIO-ONE) .LE. P1) DELTA = PNORM/P5 240 CONTINUE C C TEST FOR SUCCESSFUL ITERATION. C IF (RATIO .LT. P0001) GO TO 260 C C SUCCESSFUL ITERATION. UPDATE X, FVEC, AND THEIR NORMS. C DO 250 J = 1, N X(J) = WA2(J) WA2(J) = DIAG(J)*X(J) FVEC(J) = WA4(J) 250 CONTINUE XNORM = ENORM(N,WA2) FNORM = FNORM1 ITER = ITER + 1 260 CONTINUE C C DETERMINE THE PROGRESS OF THE ITERATION. C NSLOW1 = NSLOW1 + 1 IF (ACTRED .GE. P001) NSLOW1 = 0 IF (JEVAL) NSLOW2 = NSLOW2 + 1 IF (ACTRED .GE. P1) NSLOW2 = 0 C C TEST FOR CONVERGENCE. C IF (DELTA .LE. XTOL*XNORM .OR. FNORM .EQ. ZERO) INFO = 1 IF (INFO .NE. 0) GO TO 300 C C TESTS FOR TERMINATION AND STRINGENT TOLERANCES. C IF (NFEV .GE. MAXFEV) INFO = 2 IF (P1*MAX(P1*DELTA,PNORM) .LE. EPSMCH*XNORM) INFO = 3 IF (NSLOW2 .EQ. 5) INFO = 4 IF (NSLOW1 .EQ. 10) INFO = 5 IF (INFO .NE. 0) GO TO 300 C C CRITERION FOR RECALCULATING JACOBIAN C IF (NCFAIL .EQ. 2) GO TO 290 C C CALCULATE THE RANK ONE MODIFICATION TO THE JACOBIAN C AND UPDATE QTF IF NECESSARY. C DO 280 J = 1, N SUM = ZERO DO 270 I = 1, N SUM = SUM + FJAC(I,J)*WA4(I) 270 CONTINUE WA2(J) = (SUM - WA3(J))/PNORM WA1(J) = DIAG(J)*((DIAG(J)*WA1(J))/PNORM) IF (RATIO .GE. P0001) QTF(J) = SUM 280 CONTINUE C C COMPUTE THE QR FACTORIZATION OF THE UPDATED JACOBIAN. C CALL R1UPDT(N,N,R,LR,WA1,WA2,WA3,SING) CALL R1MPYQ(N,N,FJAC,LDFJAC,WA2,WA3) CALL R1MPYQ(1,N,QTF,1,WA2,WA3) C C END OF THE INNER LOOP. C JEVAL = .FALSE. GO TO 180 290 CONTINUE C C END OF THE OUTER LOOP. C GO TO 30 300 CONTINUE C C TERMINATION, EITHER NORMAL OR USER IMPOSED. C IF (IFLAG .LT. 0) INFO = IFLAG IFLAG = 0 IF (NPRINT .GT. 0) CALL FCN(N,X,FVEC,IFLAG) IF (INFO .LT. 0) CALL XERMSG ('SLATEC', 'SNSQ', + 'EXECUTION TERMINATED BECAUSE USER SET IFLAG NEGATIVE.', 1, 1) IF (INFO .EQ. 0) CALL XERMSG ('SLATEC', 'SNSQ', + 'INVALID INPUT PARAMETER.', 2, 1) IF (INFO .EQ. 2) CALL XERMSG ('SLATEC', 'SNSQ', + 'TOO MANY FUNCTION EVALUATIONS.', 9, 1) IF (INFO .EQ. 3) CALL XERMSG ('SLATEC', 'SNSQ', + 'XTOL TOO SMALL. NO FURTHER IMPROVEMENT POSSIBLE.', 3, 1) IF (INFO .GT. 4) CALL XERMSG ('SLATEC', 'SNSQ', + 'ITERATION NOT MAKING GOOD PROGRESS.', 1, 1) RETURN C C LAST CARD OF SUBROUTINE SNSQ. C END