DGESV 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.

N

          N is INTEGER


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


          matrix A.  N >= 0.

NRHS

          NRHS is INTEGER


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


          of the matrix B.  NRHS >= 0.

A

          A is DOUBLE PRECISION 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.

LDA

          LDA is INTEGER


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

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).

B

          B is DOUBLE PRECISION 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.

LDB

          LDB is INTEGER


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

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.

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

November 2011