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eigvalsym.html
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<h1 id="eigvalsym">EigValSym</h1>
<p>Compute the eigenvalues of a real symmetric matrix.</p>
<h1 id="usage">Usage</h1>
<p>call EigValSym (<code>ain</code>, <code>n</code>, <code>eval</code>, <code>ul</code>)</p>
<h1 id="parameters">Parameters</h1>
<dl>
<dt><code>ain</code> : input, real*8, dimension (<code>n</code>, <code>n</code>)</dt>
<dd>The input real symmetric matrix. By default, only the upper portion of the matrix is used.
</dd>
<dt><code>n</code> : input, integer</dt>
<dd>The rank of the matrix <code>ain</code>.
</dd>
<dt><code>eval</code> : output, real*8, dimension (<code>n</code>)</dt>
<dd>The eigenvalues of <code>ain</code>, sorted from largest to smallest.
</dd>
<dt><code>ul</code> : optional, input, character, default = <code>U</code></dt>
<dd>If <code>U</code> then the upper portion of the matrix <code>ain</code> will be used (default). If <code>L</code> then the lower portion of the matrix <code>ain</code> will be used.
</dd>
</dl>
<h1 id="description">Description</h1>
<p><code>EigValSym</code> will calculate the eigenvalues of a real symmetric matrix. By default, only the upper portion of the matrix is used, but this can be changed by the optional argument <code>ul</code>. The eigenvalues are sorted from largest to smallest. The matrix <code>ain</code> is first factorized into a tridiagonal matrix using the LAPACK routine <code>DSYTRD</code>, and then the eigenvalues are calculated by a call to <code>DSTEGR</code>.</p>
<h1 id="see-also">See also</h1>
<p><a href="eigvalvecsym.html">eigvalvecsym</a>, <a href="eigvalvecsymtri.html">eigvalvecsymtri</a></p>
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