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/* ../netlib/dla_lin_berr.f -- translated by f2c (version 20100827). 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 "FLA_f2c.h" /* > \brief \b DLA_LIN_BERR computes a component-wise relative backward error. */
/* =========== DOCUMENTATION =========== */
/* Online html documentation available at */
/* http://www.netlib.org/lapack/explore-html/ */
/* > \htmlonly */
/* > Download DLA_LIN_BERR + dependencies */
/* > <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dla_lin _berr.f"> */
/* > [TGZ]</a> */
/* > <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dla_lin _berr.f"> */
/* > [ZIP]</a> */
/* > <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dla_lin _berr.f"> */
/* > [TXT]</a> */
/* > \endhtmlonly */
/* Definition: */
/* =========== */
/* SUBROUTINE DLA_LIN_BERR ( N, NZ, NRHS, RES, AYB, BERR ) */
/* .. Scalar Arguments .. */
/* INTEGER N, NZ, NRHS */
/* .. */
/* .. Array Arguments .. */
/* DOUBLE PRECISION AYB( N, NRHS ), BERR( NRHS ) */
/* DOUBLE PRECISION RES( N, NRHS ) */
/* .. */
/* > \par Purpose: */
/* ============= */
/* > */
/* > \verbatim */
/* > */
/* > DLA_LIN_BERR computes component-wise relative backward error from */
/* > the formula */
/* > max(i) ( f2c_abs(R(i)) / ( f2c_abs(op(A_s))*f2c_abs(Y) + f2c_abs(B_s) )(i) ) */
/* > where f2c_abs(Z) is the component-wise absolute value of the matrix */
/* > or vector Z. */
/* > \endverbatim */
/* Arguments: */
/* ========== */
/* > \param[in] N */
/* > \verbatim */
/* > N is INTEGER */
/* > The number of linear equations, i.e., the order of the */
/* > matrix A. N >= 0. */
/* > \endverbatim */
/* > */
/* > \param[in] NZ */
/* > \verbatim */
/* > NZ is INTEGER */
/* > We add (NZ+1)*SLAMCH( 'Safe minimum' ) to R(i) in the numerator to */
/* > guard against spuriously zero residuals. Default value is N. */
/* > \endverbatim */
/* > */
/* > \param[in] NRHS */
/* > \verbatim */
/* > NRHS is INTEGER */
/* > The number of right hand sides, i.e., the number of columns */
/* > of the matrices AYB, RES, and BERR. NRHS >= 0. */
/* > \endverbatim */
/* > */
/* > \param[in] RES */
/* > \verbatim */
/* > RES is DOUBLE PRECISION array, dimension (N,NRHS) */
/* > The residual matrix, i.e., the matrix R in the relative backward */
/* > error formula above. */
/* > \endverbatim */
/* > */
/* > \param[in] AYB */
/* > \verbatim */
/* > AYB is DOUBLE PRECISION array, dimension (N, NRHS) */
/* > The denominator in the relative backward error formula above, i.e., */
/* > the matrix f2c_abs(op(A_s))*f2c_abs(Y) + f2c_abs(B_s). The matrices A, Y, and B */
/* > are from iterative refinement (see dla_gerfsx_extended.f). */
/* > \endverbatim */
/* > */
/* > \param[out] BERR */
/* > \verbatim */
/* > BERR is DOUBLE PRECISION array, dimension (NRHS) */
/* > The component-wise relative backward error from the formula above. */
/* > \endverbatim */
/* Authors: */
/* ======== */
/* > \author Univ. of Tennessee */
/* > \author Univ. of California Berkeley */
/* > \author Univ. of Colorado Denver */
/* > \author NAG Ltd. */
/* > \date September 2012 */
/* > \ingroup doubleOTHERcomputational */
/* ===================================================================== */
/* Subroutine */
int dla_lin_berr_(integer *n, integer *nz, integer *nrhs, doublereal *res, doublereal *ayb, doublereal *berr)
{
/* System generated locals */
integer ayb_dim1, ayb_offset, res_dim1, res_offset, i__1, i__2;
doublereal d__1;
/* Local variables */
integer i__, j;
doublereal tmp, safe1;
extern doublereal dlamch_(char *);
/* -- LAPACK computational routine (version 3.4.2) -- */
/* -- LAPACK is a software package provided by Univ. of Tennessee, -- */
/* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- */
/* September 2012 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* ===================================================================== */
/* .. 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 = dlamch_("Safe minimum");
safe1 = (*nz + 1) * safe1;
i__1 = *nrhs;
for (j = 1;
j <= i__1;
++j)
{
berr[j] = 0.;
i__2 = *n;
for (i__ = 1;
i__ <= i__2;
++i__)
{
if (ayb[i__ + j * ayb_dim1] != 0.)
{
tmp = (safe1 + (d__1 = res[i__ + j * res_dim1], f2c_abs(d__1))) / ayb[i__ + j * ayb_dim1];
/* Computing MAX */
d__1 = berr[j];
berr[j] = max(d__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;
}
/* dla_lin_berr__ */
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