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how to get average of matrices' elements?by fasoli (Beadle) 
on Nov 30, 2016 at 18:38 UTC ( #1176960=perlquestion: print w/replies, xml )  Need Help?? 
fasoli has asked for the wisdom of the Perl Monks concerning the following question: Hi again all. Thanks to your help I solved my first problem, thank you again. I'm after some feedback about a second problem I'm facing. So, first I'm opening four files that each have one 3x3 matrix in them, that looks like this
Now I want to do some basic math on the elements of the matrices, namely to get their average value (and then proceed to get the standard deviation, I haven't tried that yet). As I said they are four 3x3 test matrices, each one in a different file. These are test cases as my real matrices are thousands of lines long and the number of files is again thousands. So I'm after a new matrix that will have the average values of the four matrices, like so (first line only)  obviously the new matrix elements are filled with the sum of the elements divided by the number of the matrices, for example for the first line 1 + 2 + 1 + 3 = 7 / 4 = 1.75. Then the second element, 2 + 3 + 2 + 4 = 11 / 4 = 2.75. And the third element of the first line 3 + 4 + 3 + 5 = 15 / 4 = 3.75 and so on for all the elements, resulting in one matrix.
When I print the matrices with $line[$a][$b] they look correct, so I've commented this line out as it was used as a test to see if they look ok. The output I'm getting if I try to get the sum of the elements and then the mean, is Use of uninitialized value in addition (+) at test_SD_Wednesday.pl line 52 and a bunch of wrong numbers as sum/averages. I'm pretty sure I'm screwing something up badly but I can't figure out what. Any hints please? I'm starting to get scared my supervisors will really shout at me or think I'm an idiot if I tell them it's taken me 10 days to have a script that doesn't work... Finally can someone comment on the indentation? Does it make sense they way I did it? It looks less messy but no clue if I got the philosophy behind it.
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