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Annotation of rpl/lapack/lapack/zgesv.f, revision 1.7

1.1       bertrand    1:       SUBROUTINE ZGESV( N, NRHS, A, LDA, IPIV, B, LDB, INFO )
                      2: *
                      3: *  -- LAPACK driver routine (version 3.2) --
                      4: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
                      5: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
                      6: *     November 2006
                      7: *
                      8: *     .. Scalar Arguments ..
                      9:       INTEGER            INFO, LDA, LDB, N, NRHS
                     10: *     ..
                     11: *     .. Array Arguments ..
                     12:       INTEGER            IPIV( * )
                     13:       COMPLEX*16         A( LDA, * ), B( LDB, * )
                     14: *     ..
                     15: *
                     16: *  Purpose
                     17: *  =======
                     18: *
                     19: *  ZGESV computes the solution to a complex system of linear equations
                     20: *     A * X = B,
                     21: *  where A is an N-by-N matrix and X and B are N-by-NRHS matrices.
                     22: *
                     23: *  The LU decomposition with partial pivoting and row interchanges is
                     24: *  used to factor A as
                     25: *     A = P * L * U,
                     26: *  where P is a permutation matrix, L is unit lower triangular, and U is
                     27: *  upper triangular.  The factored form of A is then used to solve the
                     28: *  system of equations A * X = B.
                     29: *
                     30: *  Arguments
                     31: *  =========
                     32: *
                     33: *  N       (input) INTEGER
                     34: *          The number of linear equations, i.e., the order of the
                     35: *          matrix A.  N >= 0.
                     36: *
                     37: *  NRHS    (input) INTEGER
                     38: *          The number of right hand sides, i.e., the number of columns
                     39: *          of the matrix B.  NRHS >= 0.
                     40: *
                     41: *  A       (input/output) COMPLEX*16 array, dimension (LDA,N)
                     42: *          On entry, the N-by-N coefficient matrix A.
                     43: *          On exit, the factors L and U from the factorization
                     44: *          A = P*L*U; the unit diagonal elements of L are not stored.
                     45: *
                     46: *  LDA     (input) INTEGER
                     47: *          The leading dimension of the array A.  LDA >= max(1,N).
                     48: *
                     49: *  IPIV    (output) INTEGER array, dimension (N)
                     50: *          The pivot indices that define the permutation matrix P;
                     51: *          row i of the matrix was interchanged with row IPIV(i).
                     52: *
                     53: *  B       (input/output) COMPLEX*16 array, dimension (LDB,NRHS)
                     54: *          On entry, the N-by-NRHS matrix of right hand side matrix B.
                     55: *          On exit, if INFO = 0, the N-by-NRHS solution matrix X.
                     56: *
                     57: *  LDB     (input) INTEGER
                     58: *          The leading dimension of the array B.  LDB >= max(1,N).
                     59: *
                     60: *  INFO    (output) INTEGER
                     61: *          = 0:  successful exit
                     62: *          < 0:  if INFO = -i, the i-th argument had an illegal value
                     63: *          > 0:  if INFO = i, U(i,i) is exactly zero.  The factorization
                     64: *                has been completed, but the factor U is exactly
                     65: *                singular, so the solution could not be computed.
                     66: *
                     67: *  =====================================================================
                     68: *
                     69: *     .. External Subroutines ..
                     70:       EXTERNAL           XERBLA, ZGETRF, ZGETRS
                     71: *     ..
                     72: *     .. Intrinsic Functions ..
                     73:       INTRINSIC          MAX
                     74: *     ..
                     75: *     .. Executable Statements ..
                     76: *
                     77: *     Test the input parameters.
                     78: *
                     79:       INFO = 0
                     80:       IF( N.LT.0 ) THEN
                     81:          INFO = -1
                     82:       ELSE IF( NRHS.LT.0 ) THEN
                     83:          INFO = -2
                     84:       ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
                     85:          INFO = -4
                     86:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
                     87:          INFO = -7
                     88:       END IF
                     89:       IF( INFO.NE.0 ) THEN
                     90:          CALL XERBLA( 'ZGESV ', -INFO )
                     91:          RETURN
                     92:       END IF
                     93: *
                     94: *     Compute the LU factorization of A.
                     95: *
                     96:       CALL ZGETRF( N, N, A, LDA, IPIV, INFO )
                     97:       IF( INFO.EQ.0 ) THEN
                     98: *
                     99: *        Solve the system A*X = B, overwriting B with X.
                    100: *
                    101:          CALL ZGETRS( 'No transpose', N, NRHS, A, LDA, IPIV, B, LDB,
                    102:      $                INFO )
                    103:       END IF
                    104:       RETURN
                    105: *
                    106: *     End of ZGESV
                    107: *
                    108:       END