Hi Luis, The key (if you’ll forgive the pun) is the behaviour of the “det” function, which is (at this writing) defined in Basic/MatrixOps/matrixops.pd as:
sub det { my($x) = shift; my($opt) = shift; $opt = {} unless defined($opt); my($lu,$perm,$par); if(exists ($opt->{lu}) and (ref $opt->{lu} eq 'ARRAY')) { ($lu,$perm,$par) = @{$opt->{lu}}; } else { ($lu,$perm,$par) = lu_decomp($x); $opt->{lu} = [$lu,$perm,$par] if(exists($opt->{lu})); } ( (defined $lu) ? $lu->diagonal(0,1)->prodover * $par : 0 ); } You will see the last line returns a Perl scalar 0 if the $lu came back undefined, otherwise it will do a prodover on the diagonal, which returns a PDL ndarray. Here is my slightly-modified version of your script: use strict; use warnings; use feature 'say'; use PDL; my $m1=pdl[[-2,-2,-2], [-1,-2,-2], [0,-2,-2]]; my $m2=pdl[[-2,-2,-2],[-1,-1,-2],[0,0,-2]]; for($m1, $m2){ my $det = $_->det(my $opt={lu=>undef}); say "Got det=$det (Ref=@{[ref $det]}) lu=(@{$opt->{lu}}) for Matrix=$_"; } I will look in a while at why the lu_decomp is behaving differently for the two matrices. It is almost certainly a bug. Best regards, Ed From: Luis Mochan<mailto:moc...@icf.unam.mx> Sent: 11 February 2023 04:20 To: perldl<mailto:pdl-general@lists.sourceforge.net>; perldl<mailto:pdl-de...@lists.sourceforge.net> Subject: [Pdl-devel] inconsistent determinant I found a curious situation when running pdl, as illustrated in the following example. I build two singular 3x3 matrices and calculate their determinant, which is zero. However, in one case I get a PDL scalar and in the other I get a Perl scalar. I don't know why the different behaviour: # Program use v5.36; use PDL; my $m1=pdl[[-2,-2,-2], [-1,-2,-2], [0,-2,-2]]; my $m2=pdl[[-2,-2,-2],[-1,-1,-2],[0,0,-2]]; for($m1, $m2){ say "Matrix=$_", "Det=", $_->det, "\nRef=", ref $_->det; } #Results: Matrix= [ [-2 -2 -2] [-1 -2 -2] [ 0 -2 -2] ] Det=0 Ref=PDL Matrix= [ [-2 -2 -2] [-1 -1 -2] [ 0 0 -2] ] Det=0 Ref= I'm currently running PDL v2.081 under Perl 5.36 in Linux/testing. Best regards, Luis -- o W. Luis Mochán, | tel:(52)(777)329-1734 /<(*) Instituto de Ciencias Físicas, UNAM | fax:(52)(777)317-5388 `>/ /\ Av. Universidad s/n CP 62210 | (*)/\/ \ Cuernavaca, Morelos, México | moc...@fis.unam.mx /\_/\__/ GPG: 791EB9EB, C949 3F81 6D9B 1191 9A16 C2DF 5F0A C52B 791E B9EB _______________________________________________ pdl-devel mailing list pdl-de...@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/pdl-devel
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