* F04BFF Example Program Text * Mark 21 Release. NAG Copyright 2004. * .. Parameters .. INTEGER NIN, NOUT PARAMETER (NIN=5,NOUT=6) INTEGER KDMAX, NMAX, NRHSMX PARAMETER (KDMAX=4,NMAX=8,NRHSMX=2) INTEGER LDAB, LDB PARAMETER (LDAB=KDMAX+1,LDB=NMAX) CHARACTER UPLO PARAMETER (UPLO='U') * .. Local Scalars .. DOUBLE PRECISION ERRBND, RCOND INTEGER I, IERR, IFAIL, J, KD, N, NRHS * .. Local Arrays .. DOUBLE PRECISION AB(LDAB,NMAX), B(LDB,NRHSMX) * .. External Subroutines .. EXTERNAL F04BFF, X04CAF * .. Intrinsic Functions .. INTRINSIC MAX, MIN * .. Executable Statements .. WRITE (NOUT,*) 'F04BFF Example Program Results' WRITE (NOUT,*) * Skip heading in data file READ (NIN,*) READ (NIN,*) N, KD, NRHS IF (N.LE.NMAX .AND. KD.LE.KDMAX .AND. NRHS.LE.NRHSMX) THEN * * Read the upper or lower triangular part of the band matrix A * from data file * IF (UPLO.EQ.'U') THEN DO 20 I = 1, N READ (NIN,*) (AB(KD+1+I-J,J),J=I,MIN(N,I+KD)) 20 CONTINUE ELSE IF (UPLO.EQ.'L') THEN DO 40 I = 1, N READ (NIN,*) (AB(1+I-J,J),J=MAX(1,I-KD),I) 40 CONTINUE END IF * * Read B from data file * READ (NIN,*) ((B(I,J),J=1,NRHS),I=1,N) * * Solve the equations AX = B for X * IFAIL = -1 CALL F04BFF(UPLO,N,KD,NRHS,AB,LDAB,B,LDB,RCOND,ERRBND,IFAIL) * IF (IFAIL.EQ.0) THEN * * Print solution, estimate of condition number and approximate * error bound * IERR = 0 CALL X04CAF('General',' ',N,NRHS,B,LDB,'Solution',IERR) * WRITE (NOUT,*) WRITE (NOUT,*) 'Estimate of condition number' WRITE (NOUT,99999) 1.0D0/RCOND WRITE (NOUT,*) WRITE (NOUT,*) + 'Estimate of error bound for computed solutions' WRITE (NOUT,99999) ERRBND ELSE IF (IFAIL.EQ.N+1) THEN * * Matrix A is numerically singular. Print estimate of * reciprocal of condition number and solution * WRITE (NOUT,*) WRITE (NOUT,*) 'Estimate of reciprocal of condition number' WRITE (NOUT,99999) RCOND * WRITE (NOUT,*) IERR = 0 CALL X04CAF('General',' ',N,NRHS,B,LDB,'Solution',IERR) * ELSE IF (IFAIL.GT.0 .AND. IFAIL.LE.N) THEN * * The matrix A is not positive definite to working precision * WRITE (NOUT,99998) 'The leading minor of order ', IFAIL, + ' is not positive definite' END IF ELSE WRITE (NOUT,*) + 'One or more of NMAX, KDMAX and NRHSMX is too small' END IF STOP * 99999 FORMAT (6X,1P,E9.1) 99998 FORMAT (1X,A,I3,A) END