Talk:QR decomposition: Difference between revisions
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The task is misleading at best. Some answers successfully compute Householder projections, |
The task is misleading at best. Some answers successfully compute Householder projections, |
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but, like the task description, they fail to understand that a QR decomposition is never |
but, like the task description, they fail to understand that a QR decomposition is never |
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computed this way, as this would be too much time- and space- consumming. |
computed this way, as this would be too much time- and space- consumming. |
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''u'' of array ''I- s uu''' is ever stored, together with ''s'' or something equivalent to ''s''. |
Only the vector ''u'' of array ''I - s uu''' is ever stored, together with ''s'' or something equivalent to ''s''. |
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And both ''Q'' and ''R'' are stored in ''A'' in the process, with only a supplementary vector. |
And both ''Q'' and ''R'' are stored in ''A'' in the process, with only a supplementary vector. |
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LINPACK and LAPACK are of course no exception, though they handle the question in a [slightly |
LINPACK and LAPACK are of course no exception, though they handle the question in a [http://stackoverflow.com/questions/3031215/mystified-by-qr-q-what-is-an-orthonormal-matrix-in-compact-form slightly |
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different way]. |
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different way](http://stackoverflow.com/questions/3031215/mystified-by-qr-q-what-is-an-orthonormal-matrix-in-compact-form). |
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And when solving a system given an already computed QR in packed form, there are also ways to do |
And when solving a system given an already computed QR in packed form, there are also ways to do |
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