I apologize in advance for being slightly off topic.  I was hoping someone on this list would know the answer to my question.<div><br></div><div>I have implemented a double-shift QR algorithm in three languages, C++, Python, and MATLAB.  The reason for the Python and MATLAB implementations are to check my C++ version which uses the boost bindings to LAPACK.  My problem is that none of the implementations give the same result.  Even the QR decompositions are different.  I know the QR decomposition isn&#39;t unique, but it is only not-unique up to multiplying by -1.  At least that&#39;s the way I understand it.</div>
<div><br></div><div>Is anyone aware of how I might go about testing my algorithm?  Is there a published example I can compare with?</div><div><br></div><div>Thanks,</div><div>Jeremy</div>