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/* cpbequ.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 cpbequ_(char *uplo, integer *n, integer *kd, complex *ab,
integer *ldab, real *s, real *scond, real *amax, integer *info)
{
/* System generated locals */
integer ab_dim1, ab_offset, i__1, i__2;
real r__1, r__2;
/* Builtin functions */
double sqrt(doublereal);
/* Local variables */
integer i__, j;
real smin;
extern logical lsame_(char *, char *);
logical upper;
extern /* Subroutine */ int xerbla_(char *, integer *);
/* -- LAPACK routine (version 3.2) -- */
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/* November 2006 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* CPBEQU computes row and column scalings intended to equilibrate a */
/* Hermitian positive definite band matrix A and reduce its condition */
/* number (with respect to the two-norm). S contains the scale factors, */
/* S(i) = 1/sqrt(A(i,i)), chosen so that the scaled matrix B with */
/* elements B(i,j) = S(i)*A(i,j)*S(j) has ones on the diagonal. This */
/* choice of S puts the condition number of B within a factor N of the */
/* smallest possible condition number over all possible diagonal */
/* scalings. */
/* Arguments */
/* ========= */
/* UPLO (input) CHARACTER*1 */
/* = 'U': Upper triangular of A is stored; */
/* = 'L': Lower triangular of A is stored. */
/* N (input) INTEGER */
/* The order of the matrix A. N >= 0. */
/* KD (input) INTEGER */
/* The number of superdiagonals of the matrix A if UPLO = 'U', */
/* or the number of subdiagonals if UPLO = 'L'. KD >= 0. */
/* AB (input) COMPLEX array, dimension (LDAB,N) */
/* The upper or lower triangle of the Hermitian band matrix A, */
/* stored in the first KD+1 rows of the array. The j-th column */
/* of A is stored in the j-th column of the array AB as follows: */
/* if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j; */
/* if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+kd). */
/* LDAB (input) INTEGER */
/* The leading dimension of the array A. LDAB >= KD+1. */
/* S (output) REAL array, dimension (N) */
/* If INFO = 0, S contains the scale factors for A. */
/* SCOND (output) REAL */
/* If INFO = 0, S contains the ratio of the smallest S(i) to */
/* the largest S(i). If SCOND >= 0.1 and AMAX is neither too */
/* large nor too small, it is not worth scaling by S. */
/* AMAX (output) REAL */
/* Absolute value of largest matrix element. If AMAX is very */
/* close to overflow or very close to underflow, the matrix */
/* should be scaled. */
/* INFO (output) INTEGER */
/* = 0: successful exit */
/* < 0: if INFO = -i, the i-th argument had an illegal value. */
/* > 0: if INFO = i, the i-th diagonal element is nonpositive. */
/* ===================================================================== */
/* .. Parameters .. */
/* .. */
/* .. Local Scalars .. */
/* .. */
/* .. External Functions .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. Executable Statements .. */
/* Test the input parameters. */
/* Parameter adjustments */
ab_dim1 = *ldab;
ab_offset = 1 + ab_dim1;
ab -= ab_offset;
--s;
/* Function Body */
*info = 0;
upper = lsame_(uplo, "U");
if (! upper && ! lsame_(uplo, "L")) {
*info = -1;
} else if (*n < 0) {
*info = -2;
} else if (*kd < 0) {
*info = -3;
} else if (*ldab < *kd + 1) {
*info = -5;
}
if (*info != 0) {
i__1 = -(*info);
xerbla_("CPBEQU", &i__1);
return 0;
}
/* Quick return if possible */
if (*n == 0) {
*scond = 1.f;
*amax = 0.f;
return 0;
}
if (upper) {
j = *kd + 1;
} else {
j = 1;
}
/* Initialize SMIN and AMAX. */
i__1 = j + ab_dim1;
s[1] = ab[i__1].r;
smin = s[1];
*amax = s[1];
/* Find the minimum and maximum diagonal elements. */
i__1 = *n;
for (i__ = 2; i__ <= i__1; ++i__) {
i__2 = j + i__ * ab_dim1;
s[i__] = ab[i__2].r;
/* Computing MIN */
r__1 = smin, r__2 = s[i__];
smin = dmin(r__1,r__2);
/* Computing MAX */
r__1 = *amax, r__2 = s[i__];
*amax = dmax(r__1,r__2);
/* L10: */
}
if (smin <= 0.f) {
/* Find the first non-positive diagonal element and return. */
i__1 = *n;
for (i__ = 1; i__ <= i__1; ++i__) {
if (s[i__] <= 0.f) {
*info = i__;
return 0;
}
/* L20: */
}
} else {
/* Set the scale factors to the reciprocals */
/* of the diagonal elements. */
i__1 = *n;
for (i__ = 1; i__ <= i__1; ++i__) {
s[i__] = 1.f / sqrt(s[i__]);
/* L30: */
}
/* Compute SCOND = min(S(I)) / max(S(I)) */
*scond = sqrt(smin) / sqrt(*amax);
}
return 0;
/* End of CPBEQU */
} /* cpbequ_ */
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