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## sgesv()

subroutine sgesv | ( | integer | n,
|  | integer | nrhs,
|  | real, dimension( lda, * ) | a,
|  | integer | lda,
|  | integer, dimension( * ) | ipiv,
|  | real, dimension( ldb, * ) | b,
|  | integer | ldb,
|  | integer | info )

Download SGESV + dependencies [TGZ] [ZIP] [TXT]

Purpose:

      !>
      !> SGESV computes the solution to a real system of linear equations
      !>    A * X = B,
      !> where A is an N-by-N matrix and X and B are N-by-NRHS matrices.
      !>
      !> The LU decomposition with partial pivoting and row interchanges is
      !> used to factor A as
      !>    A = P * L * U,
      !> where P is a permutation matrix, L is unit lower triangular, and U is
      !> upper triangular.  The factored form of A is then used to solve the
      !> system of equations A * X = B.
      !>

Parameters

  [in]

  N

      !>          N is INTEGER
      !>          The number of linear equations, i.e., the order of the
      !>          matrix A.  N >= 0.
      !>

  [in]

  NRHS

      !>          NRHS is INTEGER
      !>          The number of right hand sides, i.e., the number of columns
      !>          of the matrix B.  NRHS >= 0.
      !>

  [in,out]

  A

      !>          A is REAL array, dimension (LDA,N)
      !>          On entry, the N-by-N coefficient matrix A.
      !>          On exit, the factors L and U from the factorization
      !>          A = P*L*U; the unit diagonal elements of L are not stored.
      !>

  [in]

  LDA

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

  [out]

  IPIV

      !>          IPIV is INTEGER array, dimension (N)
      !>          The pivot indices that define the permutation matrix P;
      !>          row i of the matrix was interchanged with row IPIV(i).
      !>

  [in,out]

  B

      !>          B is REAL array, dimension (LDB,NRHS)
      !>          On entry, the N-by-NRHS matrix of right hand side matrix B.
      !>          On exit, if INFO = 0, the N-by-NRHS solution matrix X.
      !>

  [in]

  LDB

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

  [out]

  INFO

      !>          INFO is INTEGER
      !>          = 0:  successful exit
      !>          < 0:  if INFO = -i, the i-th argument had an illegal value
      !>          > 0:  if INFO = i, U(i,i) is exactly zero.  The factorization
      !>                has been completed, but the factor U is exactly
      !>                singular, so the solution could not be computed.
      !>

Author
  Univ. of Tennessee
  Univ. of California Berkeley
  Univ. of Colorado Denver
  NAG Ltd.