##
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.

###
Calling Sequence

TRIRED, *
A, D, E*

###
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.

###
Example

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