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ElmerCSC
GitHub Repository: ElmerCSC/elmerfem
 Path: blob/devel/mathlibs/src/lapack/cgesv.f
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      SUBROUTINE CGESV( N, NRHS, A, LDA, IPIV, B, LDB, INFO )

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*

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*  -- LAPACK driver routine (version 3.0) --

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*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,

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*     Courant Institute, Argonne National Lab, and Rice University

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*     March 31, 1993 

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*

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*     .. Scalar Arguments ..

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      INTEGER            INFO, LDA, LDB, N, NRHS

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*     ..

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*     .. Array Arguments ..

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      INTEGER            IPIV( * )

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      COMPLEX            A( LDA, * ), B( LDB, * )

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*     ..

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*

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*  Purpose

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*  =======

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*

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*  CGESV computes the solution to a complex system of linear equations

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*     A * X = B,

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*  where A is an N-by-N matrix and X and B are N-by-NRHS matrices.

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*

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*  The LU decomposition with partial pivoting and row interchanges is

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*  used to factor A as

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*     A = P * L * U,

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*  where P is a permutation matrix, L is unit lower triangular, and U is

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*  upper triangular.  The factored form of A is then used to solve the

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*  system of equations A * X = B.

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*

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*  Arguments

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*  =========

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*

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*  N       (input) INTEGER

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*          The number of linear equations, i.e., the order of the

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*          matrix A.  N >= 0.

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*

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*  NRHS    (input) INTEGER

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*          The number of right hand sides, i.e., the number of columns

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*          of the matrix B.  NRHS >= 0.

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*

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*  A       (input/output) COMPLEX array, dimension (LDA,N)

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*          On entry, the N-by-N coefficient matrix A.

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*          On exit, the factors L and U from the factorization

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*          A = P*L*U; the unit diagonal elements of L are not stored.

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*

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*  LDA     (input) INTEGER

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*          The leading dimension of the array A.  LDA >= max(1,N).

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*

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*  IPIV    (output) INTEGER array, dimension (N)

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*          The pivot indices that define the permutation matrix P;

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*          row i of the matrix was interchanged with row IPIV(i).

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*

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*  B       (input/output) COMPLEX array, dimension (LDB,NRHS)

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*          On entry, the N-by-NRHS matrix of right hand side matrix B.

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*          On exit, if INFO = 0, the N-by-NRHS solution matrix X.

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*

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*  LDB     (input) INTEGER

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*          The leading dimension of the array B.  LDB >= max(1,N).

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*

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*  INFO    (output) INTEGER

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*          = 0:  successful exit

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*          < 0:  if INFO = -i, the i-th argument had an illegal value

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*          > 0:  if INFO = i, U(i,i) is exactly zero.  The factorization

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*                has been completed, but the factor U is exactly

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*                singular, so the solution could not be computed.

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*

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*  =====================================================================

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*

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*     .. External Subroutines ..

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      EXTERNAL           CGETRF, CGETRS, XERBLA

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*     ..

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*     .. Intrinsic Functions ..

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      INTRINSIC          MAX

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*     ..

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*     .. Executable Statements ..

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*

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*     Test the input parameters.

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*

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      INFO = 0

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      IF( N.LT.0 ) THEN

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         INFO = -1

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      ELSE IF( NRHS.LT.0 ) THEN

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         INFO = -2

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      ELSE IF( LDA.LT.MAX( 1, N ) ) THEN

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         INFO = -4

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      ELSE IF( LDB.LT.MAX( 1, N ) ) THEN

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         INFO = -7

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      END IF

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      IF( INFO.NE.0 ) THEN

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         CALL XERBLA( 'CGESV ', -INFO )

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         RETURN

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      END IF

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*

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*     Compute the LU factorization of A.

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*

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      CALL CGETRF( N, N, A, LDA, IPIV, INFO )

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      IF( INFO.EQ.0 ) THEN

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*

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*        Solve the system A*X = B, overwriting B with X.

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*

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         CALL CGETRS( 'No transpose', N, NRHS, A, LDA, IPIV, B, LDB,

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     $                INFO )

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      END IF

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      RETURN

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*

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*     End of CGESV

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*

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      END

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