++Very nice. I had been thinking about brushing up on my neural net skills (they're 20years rusty), and I've bookmarked this this will be a good starting point for using PDL to do so.

My one minor nitpick: the sigmoid function you chose, the "logistic function", has a derivative that's f(x) * (1-f(x)), not x * (1-x), so you should replace your nonlin() sub with 

sub nonlin {
    my ( $x, $deriv ) = @_;
    my $f = 1 / ( 1 + exp( -$x ) );
    return $f * ( 1 - $f ) if defined $deriv;
    return $f;
}

[download]
... It still trains with your slope, but with my slope, it gets there faster, so 10k training loops gives better results: 
Output After Training:
[
 [ 0.0007225057]
 [0.00048051061]
 [     0.999593]
 [     0.999388]
]

[download]

In reply to Re: Basic Neural Network in PDL by pryrt
in thread Basic Neural Network in PDL by mxb

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