* F07CBF Example Program Text * Mark 21 Release. NAG Copyright 2004. * .. Parameters .. INTEGER NIN, NOUT PARAMETER (NIN=5,NOUT=6) INTEGER NMAX, NRHSMX PARAMETER (NMAX=50,NRHSMX=4) INTEGER LDB, LDX PARAMETER (LDB=NMAX,LDX=NMAX) * .. Local Scalars .. DOUBLE PRECISION RCOND INTEGER I, IFAIL, INFO, J, N, NRHS * .. Local Arrays .. DOUBLE PRECISION B(LDB,NRHSMX), BERR(NRHSMX), D(NMAX), DF(NMAX), + DL(NMAX-1), DLF(NMAX-1), DU(NMAX-1), DU2(NMAX-2), + DUF(NMAX-1), FERR(NRHSMX), WORK(3*NMAX), + X(LDX,NRHSMX) INTEGER IPIV(NMAX), IWORK(NMAX) * .. External Subroutines .. EXTERNAL DGTSVX, X04CAF * .. Executable Statements .. WRITE (NOUT,*) 'F07CBF Example Program Results' WRITE (NOUT,*) * Skip heading in data file READ (NIN,*) READ (NIN,*) N, NRHS IF (N.LE.NMAX .AND. NRHS.LE.NRHSMX) THEN * * Read the tridiagonal matrix A from data file * READ (NIN,*) (DU(I),I=1,N-1) READ (NIN,*) (D(I),I=1,N) READ (NIN,*) (DL(I),I=1,N-1) * * Read the right hand matrix B * READ (NIN,*) ((B(I,J),J=1,NRHS),I=1,N) * * Solve the equations AX = B * CALL DGTSVX('No factors','No transpose',N,NRHS,DL,D,DU,DLF,DF, + DUF,DU2,IPIV,B,LDB,X,LDX,RCOND,FERR,BERR,WORK, + IWORK,INFO) * IF ((INFO.EQ.0) .OR. (INFO.EQ.N+1)) THEN * * Print solution, error bounds and condition number * 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,*) WRITE (NOUT,*) + 'Estimated forward error bounds (machine-dependent)' WRITE (NOUT,99999) (FERR(J),J=1,NRHS) WRITE (NOUT,*) WRITE (NOUT,*) 'Estimate of reciprocal condition number' WRITE (NOUT,99999) RCOND * IF (INFO.EQ.N+1) THEN WRITE (NOUT,*) WRITE (NOUT,*) + 'The matrix A is singular to working precision' END IF ELSE WRITE (NOUT,99998) 'The (', INFO, ',', INFO, ')', + ' element of the factor U is zero' END IF ELSE WRITE (NOUT,*) 'NMAX and/or NRHSMX too small' END IF * 99999 FORMAT ((3X,1P,7E11.1)) 99998 FORMAT (1X,A,I3,A,I3,A,A) END