dgbco

NAME

dgbco - (obsolete) compute the LU factorization and condition number of a general matrix A in banded storage. If the condition number is not needed then SGBFA is slightly faster. It is typical to follow a call to SGBCO with a call to SGBSL to solve Ax = b or to SGBDI to compute the determinant of A.

SYNOPSIS

  SUBROUTINE DGBCO( A, LDA, N, NSUB, NSUPER, IPIVOT, RCOND, WORK)
  INTEGER LDA, N, NSUB, NSUPER
  INTEGER IPIVOT(*)
  DOUBLE PRECISION RCOND
  DOUBLE PRECISION A(LDA,*), WORK(*)
 
  SUBROUTINE DGBCO_64( A, LDA, N, NSUB, NSUPER, IPIVOT, RCOND, WORK)
  INTEGER*8 LDA, N, NSUB, NSUPER
  INTEGER*8 IPIVOT(*)
  DOUBLE PRECISION RCOND
  DOUBLE PRECISION A(LDA,*), WORK(*)

C INTERFACE

#include <sunperf.h>

void dgbco(double *a, int lda, int n, int nsub, int nsuper, int *ipivot, double *rcond);

void dgbco_64(double *a, long lda, long n, long nsub, long nsuper, long *ipivot, double *rcond);

ARGUMENTS

* A (input/output): On entry, the matrix A. On exit, an LU factorization of the matrix A.
* LDA (input): Leading dimension of the array A as specified in a dimension or type statement. LDA >= 2 * NSUB + NSUPER + 1.
* N (input): Order of the matrix A. N >= 0.
* NSUB (input): Number of subdiagonals of A. N-1 >= NSUB >= 0 but if N = 0 then NSUB = 0.
* NSUPER (input): Number of superdiagonals of A. N-1 >= NSUPER >= 0 but if N = 0 then NSUPER = 0.
* IPIVOT (output): On exit, a vector of pivot indices.
* RCOND (output): On exit, an estimate of the reciprocal condition number of A. 0.0 <= RCOND <= 1.0. As the value of RCOND gets smaller, operations with A such as solving Ax = b may become less stable. If RCOND satisfies RCOND + 1.0 = 1.0 then A may be singular to working precision.
* WORK (workspace): Scratch array with a dimension of N.