Re^3: Abstract image registration or feature detection

Weird, perl 5.30.0 with PDL 2.019 (which is the combo that shipped with Strawberry Perl's PDL edition) doesn't give that error.

These are the outputs for my run (adding a print "perl version $]";print "PDL version $PDL::VERSION"; at the beginning to print the versions):

Mathematically speaking, a [3x3] x [3x2] is the right balance of dimensions for a successful matrix multiplication (resulting in a [3x2] matrix). The use of PDL::Matrix used to be the way to make PDL match mathematical order for the dimensions, but maybe they've changed that between 2.019 and 2.057. (I don't think I can test, because the Strawberry Perl PDL setup is rather dependent on the libraries that Strawberry bundles, and I don't know if upgrading PDL will work... maybe I'll try in a sandbox to avoid ruining my "main" installation).

I tried getting rid of the use PDL::Matrix, but then that gets rid of the mpdl command, causing errors during perl's compile stage, and I'm not sure what hoops I would need to jump through to make my script compatible with both 2.019 and 2.057.

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Re^4: Abstract image registration or feature detection by pryrt (Abbot) on Jul 04, 2022 at 20:54 UTC
Okay, 5.30.2 & PDL 2.021 and 5.32.1 & PDL 2.025 (the last pre-bundled Perl+PDL from Strawberry) both worked like my 5.30.0 & PDL 2.019. But I was able to install PDL 5.080 with Perl 5.32.1, to get slightly newer PDL but slightly older Perl than you. But it showed the same dimensional difference. So I did some debug to make it work without PDL::Matrix <Reveal this spoiler or all in this thread> This shows the 12-ish pixel error, but will hopefully work with your 2.057 (and definitely worked with my 2.080).	[reply] [d/l]
Re^4: Abstract image registration or feature detection by kikuchiyo (Hermit) on Jul 04, 2022 at 21:01 UTC
Minimal pair: `perl -MPDL -MPDL::Matrix -e '$m = mpdl [[2,0],[0,2]]; $v = vpdl [1,2]; + print $m x $v' [ [2] [4] ]` [download] vs. `perl -MPDL -MPDL::Matrix -e '$m = mpdl [[2,0],[0,2]]; $v = vpdl [1,2]; + print inv($m) x $v' Dim mismatch in matmult of [2x2] x [2x1]: 2 != 1 at /usr/lib64/perl5/v +endor_perl/PDL/Primitive.pm line 274. PDL::matmult(PDL=SCALAR(0x5600a82130e0), PDL::Matrix=SCALAR(0x5600 +a8202ba0), PDL=SCALAR(0x5600a8d718c8)) called at /usr/lib64/perl5/ven +dor_perl/PDL/Primitive.pm line 31 PDL::__ANON__(PDL=SCALAR(0x5600a82130e0), PDL::Matrix=SCALAR(0x560 +0a8202ba0), "") called at -e line 1` [download] This looks like a bug in PDL::Matrix, specifically with inv.	[reply] [d/l] [select]
Re^5: Abstract image registration or feature detection by etj (Priest) on Jul 05, 2022 at 20:51 UTC
As now noted on pryrt's excellent bug report (thank you), this will still work as expected if you switch your `inv($m)` to `$m->inv`. This will then engage PDL::Matrix's overload of `x`, which is what you need here. I would strongly encourage you not to use PDL::Matrix, because somewhat similar to PDL::Complex, it is full of gotchas. Even though after some head-scratching it became clear what exactly was happening here, it's not particularly clear how to fix it - a keyhole change to the Perl function PDL::MatrixOps::inv to make it ensure the output was the right class would resolve this exact issue. But since that uses lu_backsub for its work, and that is an eye-wateringly complicated Perl function as well, it will not be easy. That function's output variable comes from some PDL::Slices operations. If someone were minded to at least use `git bisect` to identify the commit that broke it, that would be very helpful. Even better would be a pull-request that fixes this (obviously with a test, in `t/matrix.t`), that will use our amazing CI to check it doesn't break anything else in main PDL or known downstreams. A top tip would be that `make coretest` runs `t/matrix.t`, with a very minimal build otherwise that allows a very quick dev cycle. As a hopefully practical (as well as better-performance, because it uses LAPACK) alternative, have you taken a look at PDL::LinearAlgebra?	[reply] [d/l] [select]
Re^5: Abstract image registration or feature detection by pryrt (Abbot) on Jul 05, 2022 at 19:28 UTC
kikichiyo, Thanks for that SSCCE. I included it in a bug report	[reply]
Re^4: Abstract image registration or feature detection by etj (Priest) on Jul 05, 2022 at 21:26 UTC
The way to avoid needing `mpdl` is to transpose your data, and use `pdl`, and I would recommend doing so. But as observed elsewhere, there are almost certainly out-of-the-box solutions to this particular problem.	[reply] [d/l] [select]