[pdl-commit] [SCM] pdl branch, fix_warp2d, created. v2.018-1-g0fc6c84

[Derek L. <la...@us...>]

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The branch, fix_warp2d has been created
        at  0fc6c84a39770cda590394f0d50aebd54159efa6 (commit)

- Log -----------------------------------------------------------------
commit 0fc6c84a39770cda590394f0d50aebd54159efa6
Author: Derek Lamb <la...@us...>
Date:   Fri Sep 29 12:57:09 2017 -0600

    Remove 'thresh' option in fitwarp2d.
    
    Singular-value decomposition of the basis vectors can return
    singular values that differ by 8--10 orders of magnitude. The
    default value of thresh (1e-5) would discard several of these smaller
    values.  That's a problem because the _inverses_ of the singular
    values are actually used to produce the solution in _svd. Discarding
    the largest singular values didn't seem to help either. Since it
    wasn't entirely clear why some of the singular values were being
    discarded, I commented out that line of code, and the associated
    documentation, so now we keep all of the singular values.
    
    I also added a detailed explanation of what fitwarp2d, _svd, and
    _mkbasis actually do.  And of course, some tests.
    
    If somebody with a lot of linear algebra experience is convinced
    of a a good reason to discard some of these singular values, we
    can revisit this (hence why I haven't removed the code, just
    commented it out for now).

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