Hello!
To see how J compares to other languages out there, I tried to implement
the spectral-norm [1] language benchmark in J. Part of my code [2] for
this looks like this:
NB. entry at x,y of infinite matrix A
A =: >:@:[ %@:+ -:@:(* >:)@:+
NB. get the first y by y elements of A
subA =: A"0 _~&i. M.
subA 5500 is called in the benchmark. In the beginning, my definition
for A looked like this:
A =: >:@[ %@+ + -:@* >:@+
and was about five times slower than the definition above, even though
it computes the same values. Why is that the case?
Yours,
Robert Clausecker
[1]:
http://benchmarksgame.alioth.debian.org/u32/performance.php?test=spectralnorm
[2]:
https://gist.github.com/fuzxxl/ea936084dd5038cc4c06/c0db428c351af069332d456a2c5368c5fecb8d11
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