Hi Gabor,
>
> perldl> $a = zeroes(3,3);
>
> perldl> $a(1,1) = 1
Here you want '.='. So:
perldl> $a(1,1) .= 1
works as you would expect '=' to have done. This is a limitation of
Perl syntax and was the cause for quite a bit of head scratching at an
early stage of PDL development as it was not possible to use a
subroutine as an lvalue. This is no longer the case but I don't think
this discussion has been reopened(?). Thus the '.=' was designed as
the PDL assignment operator.
Unfortunately '=' would be correct Perl syntax so I don't think it is
easy to catch the bad uses of it.
The major advantage of this is that you can operate on small bits of
your data without making copies:
perldl> $x = sequence(100, 100)
perldl> p $x((25),(30))
3025
perldl> $window = $x(25:30,30:45)
perldl> $window .= sqrt($window)
perldl> p $x((25),(30))
55
This is possibly too subtle at times though :)
Cheers,
Jarle.
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