* F07CEF 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 PARAMETER (LDB=NMAX) * .. Local Scalars .. INTEGER I, IFAIL, INFO, J, N, NRHS * .. Local Arrays .. DOUBLE PRECISION B(LDB,NRHSMX), D(NMAX), DL(NMAX-1), DU(NMAX-1), + DU2(NMAX-2) INTEGER IPIV(NMAX) * .. External Subroutines .. EXTERNAL DGTTRF, DGTTRS, X04CAF * .. Executable Statements .. WRITE (NOUT,*) 'F07CEF 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) * * Factorize the tridiagonal matrix A * CALL DGTTRF(N,DL,D,DU,DU2,IPIV,INFO) * IF (INFO.EQ.0) THEN * * Solve the equations AX = B * CALL DGTTRS('No transpose',N,NRHS,DL,D,DU,DU2,IPIV,B,LDB, + INFO) * * Print the solution * IFAIL = 0 CALL X04CAF('General',' ',N,NRHS,B,LDB,'Solution(s)',IFAIL) * ELSE WRITE (NOUT,99999) '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 (1X,A,I3,A,I3,A,A) END