can't you just multiply the PDL matrix by itself?

You can ... but it gives the result the OP doesn't want:

C:\>perl -MPDL -le "$x = pdl([0, 1], [2,3]);print $x; print $x * $x; p
+rint $x ** 2;"

[
 [0 1]
 [2 3]
]

[
 [0 1]
 [4 9]
]

[
 [0 1]
 [4 9]
]
[download]

Cheers,
Rob