Re: [Lib2geom-devel] size comparison in Affine::inverse()

[Nathan H. <nj...@nj...>]

Does it fix the bug?  I don't understand because those two algorithms
are almost equivalent (there is a slight shift in the bounds due to
nonlinearity).  In this case det should be 0.150, which is a long way
from singular.  What is mx in this case?

njh

On Mon, Jul 21, 2014 at 03:56:48PM -0400, Alvin Penner wrote:
> while investigating LP Bug 1231990, 
> https://bugs.launchpad.net/inkscape/+bug/1231990, it was found that 
> the routine Affine::inverse() in the file affine.cpp is apparently 
> refusing to calculate the inverse of the following matrix:
> 
> 0.001,    0.0
> 0.0,    150.0
> 
> The refusal is coming from the line:
> if (!rel_error_bound(determ, mx*mx))
> 
> I would like to propose that this be changed to:
> if (!rel_error_bound(std::sqrt(fabs(determ)), mx))
> so that we would be comparing two numbers which both have units of 
> length. This would be similar to a change was made in rev 2183, where 
> a similar size comparison problem was encountered (LP Bug 1309225).
> 
> Any comments?
> 
> Cheers,
> Alvin
> 
> 
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