# perl PDL

Try to learn PDL again. seems the API is not very friendly, compared to Numpy. The doc in MetaCPAN is not very polish either. (Maybe I should try to update?)

```
use v5.20;
use PDL;
# basic matrix calculation
# see PDL::Primitive
my $v1 = pdl([42,52,48,58]);
say $v1;
my $v2 = pdl( [4,5,4,3]);
say $v2;
my $x = pdl([$v1, $v2]);
say $x;
# ($mean,$prms,$median,$min,$max,$adev,$rms) = statsover($piddle, $weights);
my @statsover = statsover($x);
say $_ for @statsover;
# ($mean,$prms,$median,$min,$max,$adev,$rms) = stats($piddle,[$weights]);
my @stats = stats($x);
say $_ for @stats;
```

TODO: how to calculate cov?

in the future, try to use PDL to implement some machine learning algorithm