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CTRRFS(1) LAPACK routine (version 3.2) CTRRFS(1)

NAME

CTRRFS - provides error bounds and backward error estimates for the solution to a system of linear equations with a triangular coefficient matrix

SYNOPSIS

UPLO, TRANS, DIAG, N, NRHS, A, LDA, B, LDB, X, LDX, FERR, BERR, WORK, RWORK, INFO )

CHARACTER DIAG, TRANS, UPLO INTEGER INFO, LDA, LDB, LDX, N, NRHS REAL BERR( * ), FERR( * ), RWORK( * ) COMPLEX A( LDA, * ), B( LDB, * ), WORK( * ), X( LDX, * )

PURPOSE

CTRRFS provides error bounds and backward error estimates for the solution to a system of linear equations with a triangular coefficient matrix. The solution matrix X must be computed by CTRTRS or some other means before entering this routine. CTRRFS does not do iterative refinement because doing so cannot improve the backward error.

ARGUMENTS

= 'U': A is upper triangular;
= 'L': A is lower triangular.

Specifies the form of the system of equations:
= 'N': A * X = B (No transpose)
= 'T': A**T * X = B (Transpose)
= 'C': A**H * X = B (Conjugate transpose)

= 'N': A is non-unit triangular;
= 'U': A is unit triangular.
The order of the matrix A. N >= 0.
The number of right hand sides, i.e., the number of columns of the matrices B and X. NRHS >= 0.
The triangular matrix A. If UPLO = 'U', the leading N-by-N upper triangular part of the array A contains the upper triangular matrix, and the strictly lower triangular part of A is not referenced. If UPLO = 'L', the leading N-by-N lower triangular part of the array A contains the lower triangular matrix, and the strictly upper triangular part of A is not referenced. If DIAG = 'U', the diagonal elements of A are also not referenced and are assumed to be 1.
The leading dimension of the array A. LDA >= max(1,N).
The right hand side matrix B.
The leading dimension of the array B. LDB >= max(1,N).
The solution matrix X.
The leading dimension of the array X. LDX >= max(1,N).
The estimated forward error bound for each solution vector X(j) (the j-th 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.
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).
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
November 2008 LAPACK routine (version 3.2)