#include "blaswrap.h"
/* dptt01.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"

/* Subroutine */ int dptt01_(integer *n, doublereal *d__, doublereal *e, 
	doublereal *df, doublereal *ef, doublereal *work, doublereal *resid)
{
    /* System generated locals */
    integer i__1;
    doublereal d__1, d__2, d__3, d__4, d__5;

    /* Local variables */
    static integer i__;
    static doublereal de, eps, anorm;
    extern doublereal dlamch_(char *);


/*  -- LAPACK test routine (version 3.1) --   
       Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..   
       November 2006   


    Purpose   
    =======   

    DPTT01 reconstructs a tridiagonal matrix A from its L*D*L'   
    factorization and computes the residual   
       norm(L*D*L' - A) / ( n * norm(A) * EPS ),   
    where EPS is the machine epsilon.   

    Arguments   
    =========   

    N       (input) INTEGTER   
            The order of the matrix A.   

    D       (input) DOUBLE PRECISION array, dimension (N)   
            The n diagonal elements of the tridiagonal matrix A.   

    E       (input) DOUBLE PRECISION array, dimension (N-1)   
            The (n-1) subdiagonal elements of the tridiagonal matrix A.   

    DF      (input) DOUBLE PRECISION array, dimension (N)   
            The n diagonal elements of the factor L from the L*D*L'   
            factorization of A.   

    EF      (input) DOUBLE PRECISION array, dimension (N-1)   
            The (n-1) subdiagonal elements of the factor L from the   
            L*D*L' factorization of A.   

    WORK    (workspace) DOUBLE PRECISION array, dimension (2*N)   

    RESID   (output) DOUBLE PRECISION   
            norm(L*D*L' - A) / (n * norm(A) * EPS)   

    =====================================================================   


       Quick return if possible   

       Parameter adjustments */
    --work;
    --ef;
    --df;
    --e;
    --d__;

    /* Function Body */
    if (*n <= 0) {
	*resid = 0.;
	return 0;
    }

    eps = dlamch_("Epsilon");

/*     Construct the difference L*D*L' - A. */

    work[1] = df[1] - d__[1];
    i__1 = *n - 1;
    for (i__ = 1; i__ <= i__1; ++i__) {
	de = df[i__] * ef[i__];
	work[*n + i__] = de - e[i__];
	work[i__ + 1] = de * ef[i__] + df[i__ + 1] - d__[i__ + 1];
/* L10: */
    }

/*     Compute the 1-norms of the tridiagonal matrices A and WORK. */

    if (*n == 1) {
	anorm = d__[1];
	*resid = abs(work[1]);
    } else {
/* Computing MAX */
	d__2 = d__[1] + abs(e[1]), d__3 = d__[*n] + (d__1 = e[*n - 1], abs(
		d__1));
	anorm = max(d__2,d__3);
/* Computing MAX */
	d__4 = abs(work[1]) + (d__1 = work[*n + 1], abs(d__1)), d__5 = (d__2 =
		 work[*n], abs(d__2)) + (d__3 = work[(*n << 1) - 1], abs(d__3) );
	*resid = max(d__4,d__5);
	i__1 = *n - 1;
	for (i__ = 2; i__ <= i__1; ++i__) {
/* Computing MAX */
	    d__3 = anorm, d__4 = d__[i__] + (d__1 = e[i__], abs(d__1)) + (
		    d__2 = e[i__ - 1], abs(d__2));
	    anorm = max(d__3,d__4);
/* Computing MAX */
	    d__4 = *resid, d__5 = (d__1 = work[i__], abs(d__1)) + (d__2 = 
		    work[*n + i__ - 1], abs(d__2)) + (d__3 = work[*n + i__], 
		    abs(d__3));
	    *resid = max(d__4,d__5);
/* L20: */
	}
    }

/*     Compute norm(L*D*L' - A) / (n * norm(A) * EPS) */

    if (anorm <= 0.) {
	if (*resid != 0.) {
	    *resid = 1. / eps;
	}
    } else {
	*resid = *resid / (doublereal) (*n) / anorm / eps;
    }

    return 0;

/*     End of DPTT01 */

} /* dptt01_ */