The sumover part works, and produces the output array that is the appropriate indexes... brilliant!
When I replace sumover($a==$b) with any($a==$b) I get an error though....

perldl> $z = which(any($a == $b));
Can't call method "flat" without a package or object reference at /usr
+/lib64/perl5/site_perl/5.8.8/x86_64-linux-thread-multi/PDL/Primitive.
+pm line 1962, <STDIN> line 20.
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