DGBSL(3)

SYNOPSIS
SUBROUTINE DGBSL (ABD, LDA, N, ML, MU, IPVT, B, JOB)

NAME
dgbsl - Solve the real band system A*X=B or TRANS(A)*X=B using the factors computed by DGBCO or DGBFA.

LIBRARY
SLATEC (LINPACK)

CATEGORY
D2A2

TYPE
DOUBLE PRECISION (SGBSL-S, DGBSL-D, CGBSL-C)

KEYWORDS
BANDED, LINEAR ALGEBRA, LINPACK, MATRIX, SOLVE

AUTHOR
Moler, C. B., (U. of New Mexico)

DESCRIPTION
DGBSL solves the double precision band system A * X = B or TRANS(A) * X = B using the factors computed by DGBCO or DGBFA. On Entry ABD DOUBLE PRECISION(LDA, N) the output from DGBCO or DGBFA. LDA INTEGER the leading dimension of the array ABD . N INTEGER the order of the original matrix. ML INTEGER number of diagonals below the main diagonal. MU INTEGER number of diagonals above the main diagonal. IPVT INTEGER(N) the pivot vector from DGBCO or DGBFA. B DOUBLE PRECISION(N) the right hand side vector. JOB INTEGER = 0 to solve A*X = B , = nonzero to solve TRANS(A)*X = B , where TRANS(A) is the transpose. On Return B the solution vector X . Error Condition A division by zero will occur if the input factor contains a zero on the diagonal. Technically this indicates singularity but it is often caused by improper arguments or improper setting of LDA . It will not occur if the subroutines are called correctly and if DGBCO has set RCOND .GT. 0.0 or DGBFA has set INFO .EQ. 0 . To compute INVERSE(A) * C where C is a matrix with P columns CALL DGBCO(ABD,LDA,N,ML,MU,IPVT,RCOND,Z) IF (RCOND is too small) GO TO ... DO 10 J = 1, P CALL DGBSL(ABD,LDA,N,ML,MU,IPVT,C(1,J),0) 10 CONTINUE

REFERENCES
J. J. Dongarra, J. R. Bunch, C. B. Moler, and G. W. Stewart, LINPACK Users' Guide, SIAM, 1979.

ROUTINES CALLED
DAXPY, DDOT

REVISION HISTORY (YYMMDD)
780814 DATE WRITTEN
890531 Changed all specific intrinsics to generic. (WRB)
890831 Modified array declarations. (WRB)
890831 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
900326 Removed duplicate information from DESCRIPTION section. (WRB)
920501 Reformatted the REFERENCES section. (WRB)