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NAME
     sgeco - compute the LU factorization and estimate the condi-
     tion  number of a general matrix A.  If the condition number
     is not needed then xGEFA is slightly faster.  It is  typical
     to follow a call to xGECO with a call to xGESL to solve Ax =
     b or to xGEDI to compute the determinant and inverse of A.

SYNOPSIS
     SUBROUTINE DGECO (DA, LDA, N, IPIVOT, DRCOND, DWORK)

     SUBROUTINE SGECO (SA, LDA, N, IPIVOT, SRCOND, SWORK)

     SUBROUTINE ZGECO (ZA, LDA, N, IPIVOT, DRCOND, ZWORK)

     SUBROUTINE CGECO (CA, LDA, N, IPIVOT, SRCOND, CWORK)



     #include <sunperf.h>

     void dgeco(double *da, int lda, int n, int  *ipivot,  double
               *rcond) ;

     void sgeco(float *sa, int lda, int  n,  int  *ipivot,  float
               *rcond) ;

     void zgeco(doublecomplex *za, int lda, int n,  int  *ipivot,
               double *rcond) ;

     void cgeco(complex *ca, int lda, int n, int  *ipivot,  float
               *rcond) ;

ARGUMENTS
     xA        On entry, the matrix A.  On exit, an LU factoriza-
               tion of A.

     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    On exit, a vector of pivot indices.

     xRCOND    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.

     xWORK     Scratch array with a dimension of N.

SAMPLE PROGRAM
           PROGRAM TEST
           IMPLICIT NONE
     C
           INTEGER           IAXEQB, LDA, LDB, N
           PARAMETER        (IAXEQB = 0)
           PARAMETER        (N = 3)
           PARAMETER        (LDA = N)
           PARAMETER        (LDB = LDA)
           DOUBLE PRECISION  A(LDA,N), B(LDB), RCOND, WORK(N)
           INTEGER           ICOL, IPIVOT(N), IROW, JOB
     C
           EXTERNAL          DGECO, 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 /
           PRINT 1000
           PRINT 1010, ((A(IROW,ICOL), ICOL = 1, N), IROW = 1, N)
           PRINT 1020
           PRINT 1030, B
           CALL DGECO (A, LDA, N, IPIVOT, RCOND, WORK)
           PRINT 1040, RCOND
           IF ((RCOND + 1.0D0) .EQ. 1.0D0) THEN
             PRINT 1060
           END IF
           JOB = IAXEQB
           CALL DGESL (A, LDA, N, IPIVOT, B, JOB)
           PRINT 1050
           PRINT 1030, B
     C
      1000 FORMAT (1X, 'A:')
      1010 FORMAT (3(3X, F4.1))
      1020 FORMAT (/1X, 'b:')
      1030 FORMAT (3X, F4.1)
      1040 FORMAT (/1X, 'Estimated reciprocal condition number:', F7.4)
      1050 FORMAT (/1X, 'A**(-1) * b:')
      1060 FORMAT (1X, 'A may be singular to working precision.')
     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

      Estimated reciprocal condition number: 0.1429

      A**(-1) * b:
         3.0
         3.0
         3.0

Партнёры:

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