/* This software was developed by Bruce Hendrickson and Robert Leland   *
 * at Sandia National Laboratories under US Department of Energy        *
 * contract DE-AC04-76DP00789 and is copyrighted by Sandia Corporation. */

#include <stdio.h>
#include "defs.h"
#include "structs.h"

/* Check an eigenpair of A by direct multiplication.  */
double    checkeig(err, A, y, n, lambda, vwsqrt, work)
double   *err;
struct vtx_data **A;
double   *y;
int       n;
double    lambda;
double   *vwsqrt;
double   *work;
{
    double    resid;
    double    normy;
    double    norm();
    void      splarax(), scadd();

    splarax(err, A, n, y, vwsqrt, work);
    scadd(err, 1, n, -lambda, y);
    normy = norm(y, 1, n);
    resid = norm(err, 1, n) / normy;
    return (resid);
}