dgerfs (l)  Linux Manuals
dgerfs: improves the computed solution to a system of linear equations and provides error bounds and backward error estimates for the solution
NAME
DGERFS  improves the computed solution to a system of linear equations and provides error bounds and backward error estimates for the solutionSYNOPSIS
 SUBROUTINE DGERFS(
 TRANS, N, NRHS, A, LDA, AF, LDAF, IPIV, B, LDB, X, LDX, FERR, BERR, WORK, IWORK, INFO )
 CHARACTER TRANS
 INTEGER INFO, LDA, LDAF, LDB, LDX, N, NRHS
 INTEGER IPIV( * ), IWORK( * )
 DOUBLE PRECISION A( LDA, * ), AF( LDAF, * ), B( LDB, * ), BERR( * ), FERR( * ), WORK( * ), X( LDX, * )
PURPOSE
DGERFS improves the computed solution to a system of linear equations and provides error bounds and backward error estimates for the solution.ARGUMENTS
 TRANS (input) CHARACTER*1

Specifies the form of the system of equations:
= aqNaq: A * X = B (No transpose)
= aqTaq: A**T * X = B (Transpose)
= aqCaq: A**H * X = B (Conjugate transpose = Transpose)  N (input) INTEGER
 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 matrices B and X. NRHS >= 0.
 A (input) DOUBLE PRECISION array, dimension (LDA,N)
 The original NbyN matrix A.
 LDA (input) INTEGER
 The leading dimension of the array A. LDA >= max(1,N).
 AF (input) DOUBLE PRECISION array, dimension (LDAF,N)
 The factors L and U from the factorization A = P*L*U as computed by DGETRF.
 LDAF (input) INTEGER
 The leading dimension of the array AF. LDAF >= max(1,N).
 IPIV (input) INTEGER array, dimension (N)
 The pivot indices from DGETRF; for 1<=i<=N, row i of the matrix was interchanged with row IPIV(i).
 B (input) DOUBLE PRECISION array, dimension (LDB,NRHS)
 The right hand side matrix B.
 LDB (input) INTEGER
 The leading dimension of the array B. LDB >= max(1,N).
 X (input/output) DOUBLE PRECISION array, dimension (LDX,NRHS)
 On entry, the solution matrix X, as computed by DGETRS. On exit, the improved solution matrix X.
 LDX (input) INTEGER
 The leading dimension of the array X. LDX >= max(1,N).
 FERR (output) DOUBLE PRECISION array, dimension (NRHS)
 The estimated forward error bound for each solution vector X(j) (the jth column of the solution matrix X). If XTRUE is the true solution corresponding to X(j), FERR(j) is an estimated upper bound for the magnitude of the largest element in (X(j)  XTRUE) divided by the magnitude of the largest element in X(j). The estimate is as reliable as the estimate for RCOND, and is almost always a slight overestimate of the true error.
 BERR (output) DOUBLE PRECISION array, dimension (NRHS)
 The componentwise relative backward error of each solution vector X(j) (i.e., the smallest relative change in any element of A or B that makes X(j) an exact solution).
 WORK (workspace) DOUBLE PRECISION array, dimension (3*N)
 IWORK (workspace) INTEGER array, dimension (N)
 INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
PARAMETERS
ITMAX is the maximum number of steps of iterative refinement.