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

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

Examples

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See the description of TRIQLfor an example using this function.

Syntax

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TRIRED, A, D, E [, /DOUBLE]

Arguments

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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

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DOUBLE

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

Version History

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4.0	Introduced

Resources and References

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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.

See Also

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EIGENVEC, ELMHES, HQR, LA_TRIRED, TRIQL