TRIRED

The TRIRED procedure uses Householder's method to reduce a real, symmetric array to tridiagonal form.

TRIRED is based on the routine tred2 described in section 11.2 of Numerical Recipes in C: The Art of Scientific Computing (Second Edition), published by Cambridge University Press, and is used by permission.

Note
If you are working with complex inputs, use the LA_TRIRED procedure instead.

Syntax

TRIRED, A, D, E [, /DOUBLE]

Arguments

A

An n by n real, symmetric array that is replaced, on exit, by the orthogonal array Q effecting the transformation. The routine TRIQL can use this result to find the eigenvectors of the array A.

D

An n-element output vector containing the diagonal elements of the tridiagonal array.

E

An n-element output vector containing the off-diagonal elements.

Keywords

DOUBLE

Set this keyword to force the computation to be done in double-precision arithmetic.

Examples

See the description of TRIQL for an example using this function.

Version History


4.0	Introduced