* F07AHF Example Program Text * Mark 15 Release. NAG Copyright 1991. * .. Parameters .. INTEGER NIN, NOUT PARAMETER (NIN=5,NOUT=6) INTEGER NMAX, NRHMAX, LDA, LDAF, LDB, LDX PARAMETER (NMAX=8,NRHMAX=NMAX,LDA=NMAX,LDAF=NMAX,LDB=NMAX, + LDX=NMAX) CHARACTER TRANS PARAMETER (TRANS='N') * .. Local Scalars .. INTEGER I, IFAIL, INFO, J, N, NRHS * .. Local Arrays .. DOUBLE PRECISION A(LDA,NMAX), AF(LDAF,NMAX), B(LDB,NRHMAX), + BERR(NRHMAX), FERR(NRHMAX), WORK(3*NMAX), + X(LDX,NMAX) INTEGER IPIV(NMAX), IWORK(NMAX) * .. External Subroutines .. EXTERNAL DGERFS, DGETRF, DGETRS, F06QFF, X04CAF * .. Executable Statements .. WRITE (NOUT,*) 'F07AHF Example Program Results' * Skip heading in data file READ (NIN,*) READ (NIN,*) N, NRHS IF (N.LE.NMAX .AND. NRHS.LE.NRHMAX) THEN * * Read A and B from data file, and copy A to AF and B to X * READ (NIN,*) ((A(I,J),J=1,N),I=1,N) READ (NIN,*) ((B(I,J),J=1,NRHS),I=1,N) * CALL F06QFF('General',N,N,A,LDA,AF,LDAF) * CALL F06QFF('General',N,NRHS,B,LDB,X,LDX) * * Factorize A in the array AF * CALL DGETRF(N,N,AF,LDAF,IPIV,INFO) * WRITE (NOUT,*) IF (INFO.EQ.0) THEN * * Compute solution in the array X * CALL DGETRS(TRANS,N,NRHS,AF,LDAF,IPIV,X,LDX,INFO) * * Improve solution, and compute backward errors and * estimated bounds on the forward errors * CALL DGERFS(TRANS,N,NRHS,A,LDA,AF,LDAF,IPIV,B,LDB,X,LDX, + FERR,BERR,WORK,IWORK,INFO) * * Print solution * IFAIL = 0 * CALL X04CAF('General',' ',N,NRHS,X,LDX,'Solution(s)',IFAIL) * WRITE (NOUT,*) WRITE (NOUT,*) 'Backward errors (machine-dependent)' WRITE (NOUT,99999) (BERR(J),J=1,NRHS) WRITE (NOUT,*) + 'Estimated forward error bounds (machine-dependent)' WRITE (NOUT,99999) (FERR(J),J=1,NRHS) ELSE WRITE (NOUT,*) 'The factor U is singular' END IF END IF STOP * 99999 FORMAT ((3X,1P,7E11.1)) END