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/* sla_lin_berr.f -- translated by f2c (version 20061008).
You must link the resulting object file with libf2c:
on Microsoft Windows system, link with libf2c.lib;
on Linux or Unix systems, link with .../path/to/libf2c.a -lm
or, if you install libf2c.a in a standard place, with -lf2c -lm
-- in that order, at the end of the command line, as in
cc *.o -lf2c -lm
Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
http://www.netlib.org/f2c/libf2c.zip
*/
#include "f2c.h"
#include "blaswrap.h"
/* Subroutine */ int sla_lin_berr__(integer *n, integer *nz, integer *nrhs,
real *res, real *ayb, real *berr)
{
/* System generated locals */
integer ayb_dim1, ayb_offset, res_dim1, res_offset, i__1, i__2;
real r__1;
/* Local variables */
integer i__, j;
real tmp, safe1;
extern doublereal slamch_(char *);
/* -- LAPACK routine (version 3.2.1) -- */
/* -- Contributed by James Demmel, Deaglan Halligan, Yozo Hida and -- */
/* -- Jason Riedy of Univ. of California Berkeley. -- */
/* -- April 2009 -- */
/* -- LAPACK is a software package provided by Univ. of Tennessee, -- */
/* -- Univ. of California Berkeley and NAG Ltd. -- */
/* .. */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* SLA_LIN_BERR computes componentwise relative backward error from */
/* the formula */
/* max(i) ( abs(R(i)) / ( abs(op(A_s))*abs(Y) + abs(B_s) )(i) ) */
/* where abs(Z) is the componentwise absolute value of the matrix */
/* or vector Z. */
/* Arguments */
/* ========== */
/* N (input) INTEGER */
/* The number of linear equations, i.e., the order of the */
/* matrix A. N >= 0. */
/* NZ (input) INTEGER */
/* We add (NZ+1)*SLAMCH( 'Safe minimum' ) to R(i) in the numerator to */
/* guard against spuriously zero residuals. Default value is N. */
/* NRHS (input) INTEGER */
/* The number of right hand sides, i.e., the number of columns */
/* of the matrices AYB, RES, and BERR. NRHS >= 0. */
/* RES (input) REAL array, dimension (N,NRHS) */
/* The residual matrix, i.e., the matrix R in the relative backward */
/* error formula above. */
/* AYB (input) REAL array, dimension (N, NRHS) */
/* The denominator in the relative backward error formula above, i.e., */
/* the matrix abs(op(A_s))*abs(Y) + abs(B_s). The matrices A, Y, and B */
/* are from iterative refinement (see sla_gerfsx_extended.f). */
/* RES (output) REAL array, dimension (NRHS) */
/* The componentwise relative backward error from the formula above. */
/* ===================================================================== */
/* .. Local Scalars .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. External Functions .. */
/* .. */
/* .. Executable Statements .. */
/* Adding SAFE1 to the numerator guards against spuriously zero */
/* residuals. A similar safeguard is in the SLA_yyAMV routine used */
/* to compute AYB. */
/* Parameter adjustments */
--berr;
ayb_dim1 = *n;
ayb_offset = 1 + ayb_dim1;
ayb -= ayb_offset;
res_dim1 = *n;
res_offset = 1 + res_dim1;
res -= res_offset;
/* Function Body */
safe1 = slamch_("Safe minimum");
safe1 = (*nz + 1) * safe1;
i__1 = *nrhs;
for (j = 1; j <= i__1; ++j) {
berr[j] = 0.f;
i__2 = *n;
for (i__ = 1; i__ <= i__2; ++i__) {
if (ayb[i__ + j * ayb_dim1] != 0.f) {
tmp = (safe1 + (r__1 = res[i__ + j * res_dim1], dabs(r__1))) /
ayb[i__ + j * ayb_dim1];
/* Computing MAX */
r__1 = berr[j];
berr[j] = dmax(r__1,tmp);
}
/* If AYB is exactly 0.0 (and if computed by SLA_yyAMV), then we know */
/* the true residual also must be exactly 0.0. */
}
}
return 0;
} /* sla_lin_berr__ */
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