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---
:name: dtrrfs
:md5sum: b2012a0affdec5f87254e2ff9d8acb59
:category: :subroutine
:arguments:
- uplo:
:type: char
:intent: input
- trans:
:type: char
:intent: input
- diag:
:type: char
:intent: input
- n:
:type: integer
:intent: input
- nrhs:
:type: integer
:intent: input
- a:
:type: doublereal
:intent: input
:dims:
- lda
- n
- lda:
:type: integer
:intent: input
- b:
:type: doublereal
:intent: input
:dims:
- ldb
- nrhs
- ldb:
:type: integer
:intent: input
- x:
:type: doublereal
:intent: input
:dims:
- ldx
- nrhs
- ldx:
:type: integer
:intent: input
- ferr:
:type: doublereal
:intent: output
:dims:
- nrhs
- berr:
:type: doublereal
:intent: output
:dims:
- nrhs
- work:
:type: doublereal
:intent: workspace
:dims:
- 3*n
- iwork:
:type: integer
:intent: workspace
:dims:
- n
- info:
:type: integer
:intent: output
:substitutions: {}
:fortran_help: " SUBROUTINE DTRRFS( UPLO, TRANS, DIAG, N, NRHS, A, LDA, B, LDB, X, LDX, FERR, BERR, WORK, IWORK, INFO )\n\n\
* Purpose\n\
* =======\n\
*\n\
* DTRRFS provides error bounds and backward error estimates for the\n\
* solution to a system of linear equations with a triangular\n\
* coefficient matrix.\n\
*\n\
* The solution matrix X must be computed by DTRTRS or some other\n\
* means before entering this routine. DTRRFS does not do iterative\n\
* refinement because doing so cannot improve the backward error.\n\
*\n\n\
* Arguments\n\
* =========\n\
*\n\
* UPLO (input) CHARACTER*1\n\
* = 'U': A is upper triangular;\n\
* = 'L': A is lower triangular.\n\
*\n\
* TRANS (input) CHARACTER*1\n\
* Specifies the form of the system of equations:\n\
* = 'N': A * X = B (No transpose)\n\
* = 'T': A**T * X = B (Transpose)\n\
* = 'C': A**H * X = B (Conjugate transpose = Transpose)\n\
*\n\
* DIAG (input) CHARACTER*1\n\
* = 'N': A is non-unit triangular;\n\
* = 'U': A is unit triangular.\n\
*\n\
* N (input) INTEGER\n\
* The order of the matrix A. N >= 0.\n\
*\n\
* NRHS (input) INTEGER\n\
* The number of right hand sides, i.e., the number of columns\n\
* of the matrices B and X. NRHS >= 0.\n\
*\n\
* A (input) DOUBLE PRECISION array, dimension (LDA,N)\n\
* The triangular matrix A. If UPLO = 'U', the leading N-by-N\n\
* upper triangular part of the array A contains the upper\n\
* triangular matrix, and the strictly lower triangular part of\n\
* A is not referenced. If UPLO = 'L', the leading N-by-N lower\n\
* triangular part of the array A contains the lower triangular\n\
* matrix, and the strictly upper triangular part of A is not\n\
* referenced. If DIAG = 'U', the diagonal elements of A are\n\
* also not referenced and are assumed to be 1.\n\
*\n\
* LDA (input) INTEGER\n\
* The leading dimension of the array A. LDA >= max(1,N).\n\
*\n\
* B (input) DOUBLE PRECISION array, dimension (LDB,NRHS)\n\
* The right hand side matrix B.\n\
*\n\
* LDB (input) INTEGER\n\
* The leading dimension of the array B. LDB >= max(1,N).\n\
*\n\
* X (input) DOUBLE PRECISION array, dimension (LDX,NRHS)\n\
* The solution matrix X.\n\
*\n\
* LDX (input) INTEGER\n\
* The leading dimension of the array X. LDX >= max(1,N).\n\
*\n\
* FERR (output) DOUBLE PRECISION array, dimension (NRHS)\n\
* The estimated forward error bound for each solution vector\n\
* X(j) (the j-th column of the solution matrix X).\n\
* If XTRUE is the true solution corresponding to X(j), FERR(j)\n\
* is an estimated upper bound for the magnitude of the largest\n\
* element in (X(j) - XTRUE) divided by the magnitude of the\n\
* largest element in X(j). The estimate is as reliable as\n\
* the estimate for RCOND, and is almost always a slight\n\
* overestimate of the true error.\n\
*\n\
* BERR (output) DOUBLE PRECISION array, dimension (NRHS)\n\
* The componentwise relative backward error of each solution\n\
* vector X(j) (i.e., the smallest relative change in\n\
* any element of A or B that makes X(j) an exact solution).\n\
*\n\
* WORK (workspace) DOUBLE PRECISION array, dimension (3*N)\n\
*\n\
* IWORK (workspace) INTEGER array, dimension (N)\n\
*\n\
* INFO (output) INTEGER\n\
* = 0: successful exit\n\
* < 0: if INFO = -i, the i-th argument had an illegal value\n\
*\n\n\
* =====================================================================\n\
*\n"
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