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C++ Question

From: Quentin H. Spencer
Subject: C++ Question
Date: Mon, 31 Mar 2003 11:58:50 -0700
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.3) Gecko/20030314

Hello all,

I have been writing some functions in C that use the octave ComplexSVD class, and I'm having trouble understanding some strange behavior. Initially I wrote the function with the following syntax:
        ComplexSVD svd;
        svd = ComplexSVD( matrix , SVD::std);
        ComplexMatrix U = svd.left_singular_matrix();

Later I changed the syntax to the following (which mirrors the syntax used in

        ComplexSVD svd( matrix , SVD::std);
        ComplexMatrix U = svd.left_singular_matrix();

When using the first syntax, the function would usually return properly the first time, but subsequent runnings of my C++ function (and sometimes even octave's builtin svd function) often resulted in the following:

error: ComplexSVD: U not computed because type == SVD::sigma_only

This is usally followed by a segmentation fault. There could be some technicality about C++ that I don't understand here, but I don't see the different between these two implementations. Can anyone enlighten me?

Quentin Spencer

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