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NAME DGESV - compute the solution to a real system of linear equations A * X = B, SYNOPSIS SUBROUTINE DGESV( N, NRHS, A, LDA, IPIV, B, LDB, INFO ) INTEGER INFO, LDA, LDB, N, NRHS INTEGER IPIV( * ) DOUBLE PRECISION A( LDA, * ), B( LDB, * ) PURPOSE DGESV computes the solution to a real system of linear equa- tions 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 inter- changes 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. ARGUMENTS N (input) INTEGER The number of linear equations, i.e., the order of the matrix A. N >= 0. NRHS (input) INTEGER The number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0. A (input/output) 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 (input) INTEGER The leading dimension of the array A. LDA >= max(1,N). IPIV (output) INTEGER array, dimension (N) The pivot indices that define the permutation matrix P; row i of the matrix was interchanged with row IPIV(i). (LDB,NRHS) B (input/output) DOUBLE PRECISION array, dimension On entry, the N-by-NRHS matrix of right hand side matrix B. On exit, if INFO = 0, the N-by-NRHS solu- tion matrix X. LDB (input) INTEGER The leading dimension of the array B. LDB >= max(1,N). INFO (output) 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 fac- torization has been completed, but the factor U is exactly singular, so the solution could not be com- puted.