140 lines
3.8 KiB
C
140 lines
3.8 KiB
C
#include "hypre_lapack.h"
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#include "f2c.h"
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doublereal dlanst_(char *norm, integer *n, doublereal *d__, doublereal *e)
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{
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/* -- LAPACK auxiliary routine (version 3.0) --
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Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
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Courant Institute, Argonne National Lab, and Rice University
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February 29, 1992
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Purpose
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=======
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DLANST returns the value of the one norm, or the Frobenius norm, or
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the infinity norm, or the element of largest absolute value of a
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real symmetric tridiagonal matrix A.
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Description
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===========
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DLANST returns the value
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DLANST = ( max(abs(A(i,j))), NORM = 'M' or 'm'
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(
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( norm1(A), NORM = '1', 'O' or 'o'
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(
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( normI(A), NORM = 'I' or 'i'
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(
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( normF(A), NORM = 'F', 'f', 'E' or 'e'
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where norm1 denotes the one norm of a matrix (maximum column sum),
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normI denotes the infinity norm of a matrix (maximum row sum) and
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normF denotes the Frobenius norm of a matrix (square root of sum of
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squares). Note that max(abs(A(i,j))) is not a matrix norm.
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Arguments
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=========
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NORM (input) CHARACTER*1
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Specifies the value to be returned in DLANST as described
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above.
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N (input) INTEGER
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The order of the matrix A. N >= 0. When N = 0, DLANST is
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set to zero.
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D (input) DOUBLE PRECISION array, dimension (N)
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The diagonal elements of A.
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E (input) DOUBLE PRECISION array, dimension (N-1)
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The (n-1) sub-diagonal or super-diagonal elements of A.
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=====================================================================
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Parameter adjustments */
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/* Table of constant values */
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static integer c__1 = 1;
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/* System generated locals */
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integer i__1;
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doublereal ret_val, d__1, d__2, d__3, d__4, d__5;
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/* Builtin functions */
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double sqrt(doublereal);
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/* Local variables */
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static integer i__;
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static doublereal scale;
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extern logical lsame_(char *, char *);
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static doublereal anorm;
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extern /* Subroutine */ int dlassq_(integer *, doublereal *, integer *,
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doublereal *, doublereal *);
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static doublereal sum;
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--e;
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--d__;
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/* Function Body */
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if (*n <= 0) {
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anorm = 0.;
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} else if (lsame_(norm, "M")) {
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/* Find max(abs(A(i,j))). */
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anorm = (d__1 = d__[*n], abs(d__1));
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i__1 = *n - 1;
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for (i__ = 1; i__ <= i__1; ++i__) {
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/* Computing MAX */
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d__2 = anorm, d__3 = (d__1 = d__[i__], abs(d__1));
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anorm = max(d__2,d__3);
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/* Computing MAX */
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d__2 = anorm, d__3 = (d__1 = e[i__], abs(d__1));
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anorm = max(d__2,d__3);
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/* L10: */
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}
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} else if (lsame_(norm, "O") || *(unsigned char *)
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norm == '1' || lsame_(norm, "I")) {
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/* Find norm1(A). */
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if (*n == 1) {
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anorm = abs(d__[1]);
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} else {
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/* Computing MAX */
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d__3 = abs(d__[1]) + abs(e[1]), d__4 = (d__1 = e[*n - 1], abs(
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d__1)) + (d__2 = d__[*n], abs(d__2));
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anorm = max(d__3,d__4);
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i__1 = *n - 1;
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for (i__ = 2; i__ <= i__1; ++i__) {
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/* Computing MAX */
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d__4 = anorm, d__5 = (d__1 = d__[i__], abs(d__1)) + (d__2 = e[
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i__], abs(d__2)) + (d__3 = e[i__ - 1], abs(d__3));
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anorm = max(d__4,d__5);
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/* L20: */
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}
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}
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} else if (lsame_(norm, "F") || lsame_(norm, "E")) {
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/* Find normF(A). */
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scale = 0.;
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sum = 1.;
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if (*n > 1) {
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i__1 = *n - 1;
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dlassq_(&i__1, &e[1], &c__1, &scale, &sum);
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sum *= 2;
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}
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dlassq_(n, &d__[1], &c__1, &scale, &sum);
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anorm = scale * sqrt(sum);
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}
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ret_val = anorm;
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return ret_val;
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/* End of DLANST */
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} /* dlanst_ */
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