I know this isn't part of your question, but I also want to add that you should read perldoc perlvar, specifically the part on special variables $a and $b. Long story short, don't use variables with those names, they're reserved. Besides, they're horrible names. $x and $y are less horrible only because they have standard mathematical meanings.

Thus, your code should be more like this:

use strict;
use warnings; # important, too.

#-- variables and handles 
my @Matrix = map { [ (0) x 361 ] } 0..360;

#--Open the input and output files

# use 3-arg open, use lexical filehandle, don't interpolate a variable
# that doesn't need anything added to it, i.e., "$inf" is bad, but "$i
+nf-foo"
# is not, report WHY open fails, not merely that it has failed.
open my $in, '<', $foo or die "Can't read $inf: $!";

# lexical $line with minimal scope, check for definedness
# (if you have a line that is "0\n", you'll find your original code
# will terminate early).
while (defined (my $line = <IN>))
{
# usually, split ' ', $line is what you want instead of /\s+/.
# but they do slightly different things, so I'm not changing it.
# Added "my" so we create a new @result each time.
 my @result   = split(/\s+/, $line);

# I'm guessing here since I don't know where $phi and $psi really
# come from.
 my $phi = int($result[0]);
 my $psi = int($result[1]);

# use $ instead of @ to signify we want a scalar value from
# the array.  Use ++ instead of += 1 because it's more idiomatic
# though technically it's no big deal either way.
 $Matrix[$phi+180][$psi+180] ++;
   
}
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Note that you're going from angle 0 through 360, which means that you're duplicating the ends. Normally, I'd think you'd want just 0..359 - because 360 and 0 are the same angle.