cgesl(3P)

NAME

cgesl - solve the linear system Ax = b for a general matrix A, which has been LU- factored by xGECO or xGEFA, and vectors b and x.

SYNOPSIS

SUBROUTINE DGESL (DA, LDA, N, IPIVOT, DB, JOB)

SUBROUTINE SGESL (SA, LDA, N, IPIVOT, SB, JOB)

SUBROUTINE ZGESL (ZA, LDA, N, IPIVOT, ZB, JOB)

SUBROUTINE CGESL (CA, LDA, N, IPIVOT, CB, JOB)

#include <sunperf.h>

void cgesl(complex ∗ca, int lda, int n, int ∗ipivot, complex ∗cb, int job);

void dgesl(double ∗da, int lda, int n, int ∗ipivot, double ∗db, int job);

void sgesl(float ∗sa, int lda, int n, int ∗ipivot, float ∗b, int job);

void zgesl(doublecomplex ∗za, int lda, int n, int ∗ipivot, doublecomplex ∗zb, int job) ;

void cgesl(complex ∗ca, int lda, int n, int ∗ipivot, complex ∗cb, int job);

ARGUMENTS

xA LU factorization of the matrix A, as computed by xGECO or xGEFA.

LDA Leading dimension of the array A as specified in a dimension or type statement. LDA >= max(1,N).

N Order of the matrix A. N >= 0.

IPIVOT Pivot vector as computed by xGECO or xGEFA.

xB On entry, the right-hand side vector b. On exit, the solution vector x.

JOB Determines which operation the subroutine will perform:
0Solve the system Ax = b.
not 0Solve the linear system AHx = b. Note that ATx = AHx for real matrices.

SAMPLE PROGRAM

      PROGRAM TEST
      IMPLICIT NONE
C
      INTEGER           IAXEQB, LDA, LDB, N
      PARAMETER        (IAXEQB = 0)
      PARAMETER        (N = 3)
      PARAMETER        (LDA = N)
      PARAMETER        (LDB = LDA)
C
      DOUBLE PRECISION A(LDA,N), B(LDB)
      INTEGER           ICOL, INFO, IPIVOT(N), IROW, JOB
C
      EXTERNAL          DGEFA, DGESL
C
C     Initialize the array A to store the matrix A shown below.
C     Initialize the array B to store the vector b shown below.
C
C         1 2 2        15
C     A = 2 1 2    b = 15
C         2 2 1        15
C
      DATA A / 1.0D0, 3∗2.0D0, 1.0D0, 3∗2.0D0, 1.0D0 /
      DATA B / 3∗1.5D1 /
C
      PRINT 1000
      PRINT 1010, ((A(IROW,ICOL), ICOL = 1, N), IROW = 1, N)
      PRINT 1020
      PRINT 1030, B
      CALL DGEFA (A, LDA, N, IPIVOT, INFO)
      IF (INFO .EQ. 0) THEN
        JOB = IAXEQB
        CALL DGESL (A, LDA, N, IPIVOT, B, JOB)
        PRINT 1040
        PRINT 1030, B
      ELSE
        PRINT 1050, INFO
      END IF
C
1000 FORMAT (1X, ’A:’)
1010 FORMAT (3(3X, F4.1))
1020 FORMAT (/1X, ’b:’)
1030 FORMAT (1X, 2X, F4.1)
1040 FORMAT (/1X, ’A∗∗(-1)∗b’)
1050 FORMAT (1X, ’A appears singular at ’, I2)
C
      END

SAMPLE OUTPUT

A:
    1.0    2.0    2.0
    2.0    1.0    2.0
    2.0    2.0    1.0

b:
   15.0
   15.0
   15.0

A∗∗(-1)∗b
    3.0
    3.0
    3.0