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/* chetd2.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"
/* Table of constant values */
static complex c_b2 = {0.f,0.f};
static integer c__1 = 1;
/* Subroutine */ int chetd2_(char *uplo, integer *n, complex *a, integer *lda,
real *d__, real *e, complex *tau, integer *info)
{
/* System generated locals */
integer a_dim1, a_offset, i__1, i__2, i__3;
real r__1;
complex q__1, q__2, q__3, q__4;
/* Local variables */
integer i__;
complex taui;
extern /* Subroutine */ int cher2_(char *, integer *, complex *, complex *
, integer *, complex *, integer *, complex *, integer *);
complex alpha;
extern /* Complex */ VOID cdotc_(complex *, integer *, complex *, integer
*, complex *, integer *);
extern logical lsame_(char *, char *);
extern /* Subroutine */ int chemv_(char *, integer *, complex *, complex *
, integer *, complex *, integer *, complex *, complex *, integer *
), caxpy_(integer *, complex *, complex *, integer *,
complex *, integer *);
logical upper;
extern /* Subroutine */ int clarfg_(integer *, complex *, complex *,
integer *, complex *), 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 */
/* ======= */
/* CHETD2 reduces a complex Hermitian matrix A to real symmetric */
/* tridiagonal form T by a unitary similarity transformation: */
/* Q' * A * Q = T. */
/* Arguments */
/* ========= */
/* UPLO (input) CHARACTER*1 */
/* Specifies whether the upper or lower triangular part of the */
/* Hermitian matrix A is stored: */
/* = 'U': Upper triangular */
/* = 'L': Lower triangular */
/* N (input) INTEGER */
/* The order of the matrix A. N >= 0. */
/* A (input/output) COMPLEX array, dimension (LDA,N) */
/* On entry, the Hermitian matrix A. If UPLO = 'U', the leading */
/* n-by-n upper triangular part of A contains the upper */
/* triangular part of the matrix A, and the strictly lower */
/* triangular part of A is not referenced. If UPLO = 'L', the */
/* leading n-by-n lower triangular part of A contains the lower */
/* triangular part of the matrix A, and the strictly upper */
/* triangular part of A is not referenced. */
/* On exit, if UPLO = 'U', the diagonal and first superdiagonal */
/* of A are overwritten by the corresponding elements of the */
/* tridiagonal matrix T, and the elements above the first */
/* superdiagonal, with the array TAU, represent the unitary */
/* matrix Q as a product of elementary reflectors; if UPLO */
/* = 'L', the diagonal and first subdiagonal of A are over- */
/* written by the corresponding elements of the tridiagonal */
/* matrix T, and the elements below the first subdiagonal, with */
/* the array TAU, represent the unitary matrix Q as a product */
/* of elementary reflectors. See Further Details. */
/* LDA (input) INTEGER */
/* The leading dimension of the array A. LDA >= max(1,N). */
/* D (output) REAL array, dimension (N) */
/* The diagonal elements of the tridiagonal matrix T: */
/* D(i) = A(i,i). */
/* E (output) REAL array, dimension (N-1) */
/* The off-diagonal elements of the tridiagonal matrix T: */
/* E(i) = A(i,i+1) if UPLO = 'U', E(i) = A(i+1,i) if UPLO = 'L'. */
/* TAU (output) COMPLEX array, dimension (N-1) */
/* The scalar factors of the elementary reflectors (see Further */
/* Details). */
/* INFO (output) INTEGER */
/* = 0: successful exit */
/* < 0: if INFO = -i, the i-th argument had an illegal value. */
/* Further Details */
/* =============== */
/* If UPLO = 'U', the matrix Q is represented as a product of elementary */
/* reflectors */
/* Q = H(n-1) . . . H(2) H(1). */
/* Each H(i) has the form */
/* H(i) = I - tau * v * v' */
/* where tau is a complex scalar, and v is a complex vector with */
/* v(i+1:n) = 0 and v(i) = 1; v(1:i-1) is stored on exit in */
/* A(1:i-1,i+1), and tau in TAU(i). */
/* If UPLO = 'L', the matrix Q is represented as a product of elementary */
/* reflectors */
/* Q = H(1) H(2) . . . H(n-1). */
/* Each H(i) has the form */
/* H(i) = I - tau * v * v' */
/* where tau is a complex scalar, and v is a complex vector with */
/* v(1:i) = 0 and v(i+1) = 1; v(i+2:n) is stored on exit in A(i+2:n,i), */
/* and tau in TAU(i). */
/* The contents of A on exit are illustrated by the following examples */
/* with n = 5: */
/* if UPLO = 'U': if UPLO = 'L': */
/* ( d e v2 v3 v4 ) ( d ) */
/* ( d e v3 v4 ) ( e d ) */
/* ( d e v4 ) ( v1 e d ) */
/* ( d e ) ( v1 v2 e d ) */
/* ( d ) ( v1 v2 v3 e d ) */
/* where d and e denote diagonal and off-diagonal elements of T, and vi */
/* denotes an element of the vector defining H(i). */
/* ===================================================================== */
/* .. Parameters .. */
/* .. */
/* .. Local Scalars .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. External Functions .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. Executable Statements .. */
/* Test the input parameters */
/* Parameter adjustments */
a_dim1 = *lda;
a_offset = 1 + a_dim1;
a -= a_offset;
--d__;
--e;
--tau;
/* Function Body */
*info = 0;
upper = lsame_(uplo, "U");
if (! upper && ! lsame_(uplo, "L")) {
*info = -1;
} else if (*n < 0) {
*info = -2;
} else if (*lda < max(1,*n)) {
*info = -4;
}
if (*info != 0) {
i__1 = -(*info);
xerbla_("CHETD2", &i__1);
return 0;
}
/* Quick return if possible */
if (*n <= 0) {
return 0;
}
if (upper) {
/* Reduce the upper triangle of A */
i__1 = *n + *n * a_dim1;
i__2 = *n + *n * a_dim1;
r__1 = a[i__2].r;
a[i__1].r = r__1, a[i__1].i = 0.f;
for (i__ = *n - 1; i__ >= 1; --i__) {
/* Generate elementary reflector H(i) = I - tau * v * v' */
/* to annihilate A(1:i-1,i+1) */
i__1 = i__ + (i__ + 1) * a_dim1;
alpha.r = a[i__1].r, alpha.i = a[i__1].i;
clarfg_(&i__, &alpha, &a[(i__ + 1) * a_dim1 + 1], &c__1, &taui);
i__1 = i__;
e[i__1] = alpha.r;
if (taui.r != 0.f || taui.i != 0.f) {
/* Apply H(i) from both sides to A(1:i,1:i) */
i__1 = i__ + (i__ + 1) * a_dim1;
a[i__1].r = 1.f, a[i__1].i = 0.f;
/* Compute x := tau * A * v storing x in TAU(1:i) */
chemv_(uplo, &i__, &taui, &a[a_offset], lda, &a[(i__ + 1) *
a_dim1 + 1], &c__1, &c_b2, &tau[1], &c__1);
/* Compute w := x - 1/2 * tau * (x'*v) * v */
q__3.r = -.5f, q__3.i = -0.f;
q__2.r = q__3.r * taui.r - q__3.i * taui.i, q__2.i = q__3.r *
taui.i + q__3.i * taui.r;
cdotc_(&q__4, &i__, &tau[1], &c__1, &a[(i__ + 1) * a_dim1 + 1]
, &c__1);
q__1.r = q__2.r * q__4.r - q__2.i * q__4.i, q__1.i = q__2.r *
q__4.i + q__2.i * q__4.r;
alpha.r = q__1.r, alpha.i = q__1.i;
caxpy_(&i__, &alpha, &a[(i__ + 1) * a_dim1 + 1], &c__1, &tau[
1], &c__1);
/* Apply the transformation as a rank-2 update: */
/* A := A - v * w' - w * v' */
q__1.r = -1.f, q__1.i = -0.f;
cher2_(uplo, &i__, &q__1, &a[(i__ + 1) * a_dim1 + 1], &c__1, &
tau[1], &c__1, &a[a_offset], lda);
} else {
i__1 = i__ + i__ * a_dim1;
i__2 = i__ + i__ * a_dim1;
r__1 = a[i__2].r;
a[i__1].r = r__1, a[i__1].i = 0.f;
}
i__1 = i__ + (i__ + 1) * a_dim1;
i__2 = i__;
a[i__1].r = e[i__2], a[i__1].i = 0.f;
i__1 = i__ + 1;
i__2 = i__ + 1 + (i__ + 1) * a_dim1;
d__[i__1] = a[i__2].r;
i__1 = i__;
tau[i__1].r = taui.r, tau[i__1].i = taui.i;
/* L10: */
}
i__1 = a_dim1 + 1;
d__[1] = a[i__1].r;
} else {
/* Reduce the lower triangle of A */
i__1 = a_dim1 + 1;
i__2 = a_dim1 + 1;
r__1 = a[i__2].r;
a[i__1].r = r__1, a[i__1].i = 0.f;
i__1 = *n - 1;
for (i__ = 1; i__ <= i__1; ++i__) {
/* Generate elementary reflector H(i) = I - tau * v * v' */
/* to annihilate A(i+2:n,i) */
i__2 = i__ + 1 + i__ * a_dim1;
alpha.r = a[i__2].r, alpha.i = a[i__2].i;
i__2 = *n - i__;
/* Computing MIN */
i__3 = i__ + 2;
clarfg_(&i__2, &alpha, &a[min(i__3, *n)+ i__ * a_dim1], &c__1, &
taui);
i__2 = i__;
e[i__2] = alpha.r;
if (taui.r != 0.f || taui.i != 0.f) {
/* Apply H(i) from both sides to A(i+1:n,i+1:n) */
i__2 = i__ + 1 + i__ * a_dim1;
a[i__2].r = 1.f, a[i__2].i = 0.f;
/* Compute x := tau * A * v storing y in TAU(i:n-1) */
i__2 = *n - i__;
chemv_(uplo, &i__2, &taui, &a[i__ + 1 + (i__ + 1) * a_dim1],
lda, &a[i__ + 1 + i__ * a_dim1], &c__1, &c_b2, &tau[
i__], &c__1);
/* Compute w := x - 1/2 * tau * (x'*v) * v */
q__3.r = -.5f, q__3.i = -0.f;
q__2.r = q__3.r * taui.r - q__3.i * taui.i, q__2.i = q__3.r *
taui.i + q__3.i * taui.r;
i__2 = *n - i__;
cdotc_(&q__4, &i__2, &tau[i__], &c__1, &a[i__ + 1 + i__ *
a_dim1], &c__1);
q__1.r = q__2.r * q__4.r - q__2.i * q__4.i, q__1.i = q__2.r *
q__4.i + q__2.i * q__4.r;
alpha.r = q__1.r, alpha.i = q__1.i;
i__2 = *n - i__;
caxpy_(&i__2, &alpha, &a[i__ + 1 + i__ * a_dim1], &c__1, &tau[
i__], &c__1);
/* Apply the transformation as a rank-2 update: */
/* A := A - v * w' - w * v' */
i__2 = *n - i__;
q__1.r = -1.f, q__1.i = -0.f;
cher2_(uplo, &i__2, &q__1, &a[i__ + 1 + i__ * a_dim1], &c__1,
&tau[i__], &c__1, &a[i__ + 1 + (i__ + 1) * a_dim1],
lda);
} else {
i__2 = i__ + 1 + (i__ + 1) * a_dim1;
i__3 = i__ + 1 + (i__ + 1) * a_dim1;
r__1 = a[i__3].r;
a[i__2].r = r__1, a[i__2].i = 0.f;
}
i__2 = i__ + 1 + i__ * a_dim1;
i__3 = i__;
a[i__2].r = e[i__3], a[i__2].i = 0.f;
i__2 = i__;
i__3 = i__ + i__ * a_dim1;
d__[i__2] = a[i__3].r;
i__2 = i__;
tau[i__2].r = taui.r, tau[i__2].i = taui.i;
/* L20: */
}
i__1 = *n;
i__2 = *n + *n * a_dim1;
d__[i__1] = a[i__2].r;
}
return 0;
/* End of CHETD2 */
} /* chetd2_ */
|
