Expecting a 100 solutions, getting just 1

doozy has asked for the wisdom of the Perl Monks concerning the following question:

Hello Monks- I have the following script to generate a 100 trial solutions of A and B, uniformly distributed between 0 and A_max and 0 and B_max, respectively. I want to choose a trial pair of A and B which will minimize a certain error term. What I don't understand is how to "store" the 10000 trial solution pairs so they can be referred to by the script. Also, if I wanted to print the 100 solutions, e.g. for A, how can that be done? I only get 1 solution for A when I run just the t and A loops and print $A. Here's the (incomplete) code, I put a space between the lines to help readability:

 

#!/usr/bin/perl

$A_max = 1e-05, $B_max = 1e-04, $t_max = 200, $z_best = 1e+12;

for ($t=0; $t<=$t_max; $t++) {

  for ($A=0; $A<=$A_max; $A+=$A_max/100) {

    for ($B=0; $B<=$B_max; $B+=$B_max/100) {

     #something here that should refer to $i_max; $i_max = 
10000 because I expect 10000 pairs of A and B solution   pairs.

       #somehow use the 10000 trial solution pairs of $A and $B to sub
+stitute into the equation, $er_max = |A| + |B|.

     #set $er_max = $z, corresponding to the error calculated for each
+ trial solution pair. 

      for ($i=0; $i<$i_max; $i++) {  
 
        if ($z < $z_best) {

            $z_best = $z;

            $A_best = $A;

            $B_best = $B;
        }
      } 
    }
  }
}

print "$A = $A_best\n";
print "$B = $B_best\n";
[download]

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Re: Expecting a 100 solutions, getting just 1 by moritz (Cardinal) on Apr 17, 2012 at 08:35 UTC
It's hard to understand what you are trying to do. What is a "trial solution"? Is there some randomness involved? If you want to store multiple somethings, you best use an array: `my @interesting_values; for (1...1000) { my $r = rand; if ($r > 0.5) { push @interesting_values, $r; } }` [download] See also: perldata, perlintro. This part of your code: `for ($i=0; $i<$i_max; $i++) { if ($z < $z_best) {` [download] seems to be entirely useless, because you never set `$z` to anything, and there's no reason to iterate over that if-statement, since nothing in there is random or depends on `$i`. Also please Use strict and warnings and declare your variables with my. Perl 6 - the future is here, just unevenly distributed	[reply] [d/l] [select]
Re^2: Expecting a 100 solutions, getting just 1 by doozy (Initiate) on Apr 17, 2012 at 08:58 UTC
There is randomness involved because 1 value of $A is a guess. The objective is to choose a pair of guesses A and B which minimize the error term. Also, will declaring the variables with my get around the scalar property of $? Thanks for the tip about the warnings.	[reply]
Re^3: Expecting a 100 solutions, getting just 1 by moritz (Cardinal) on Apr 17, 2012 at 09:10 UTC
There is randomness involved Where? I don't see any calls to rand, or other sources of randomness in your code because 1 value of $A is a guess. A guess for what? The objective is to choose a pair of guesses A and B which minimize the error term. What's the error term? How is it calculated? Also, will declaring the variables with my get around the scalar property of $? No. You're not supposed to work around it, you are supposed to use variables starting with `@` if you want multiple values in one variable. Perl 6 - the future is here, just unevenly distributed	[reply] [d/l]
Re^4: Expecting a 100 solutions, getting just 1 by doozy (Initiate) on Apr 17, 2012 at 09:58 UTC
Re: Expecting a 100 solutions, getting just 1 by Anonymous Monk on Apr 17, 2012 at 08:44 UTC
In perl, $foo is called a scalar, it holds one and only one value. To store more than one of something, you need an array. So `#!/usr/bin/perl -- use strict; use warnings; Main( @ARGV ); exit( 0 ); sub Main { my @Solutions; ... push @Solutions, Solution( $t, $i, $A, $B ); ... print join "\n", "Top 100:", @Solutions[ 0 .. 99 ]; } sub Solution { my( $t, $i, $A, $B ) = @_; my $result = $t / $i / $A / $B + "yada yada yada"; return $result; }` [download] more on this in perlintro, the basic datatypes, three, Arrays: A Tutorial/Reference, Lexical scoping like a fox, Read this if you want to cut your development time in half! and understand that `strict` itself confers no benefits; The benefits come from avoidance of the bad practices forbidden by `strict` :) See also abs	[reply] [d/l] [select]
Re: Expecting a 100 solutions, getting just 1 by brx (Pilgrim) on Apr 17, 2012 at 09:33 UTC
`$A_max = 1e-05, $B_max = 1e-04, $t_max = 200, $z_best = 1e+12;` Wrong separator ! Should be `my $A_max = 1e-05; my $B_max = 1e-04; my $t_max = 200; $z_best = 1e+12;` You have to `use strict; use warnings;` Perlish loops are simple to read `for my $t (0 .. $_tmax) {...}` `for my $A_part (0 .. 100) { $A=$A_max*$A_part/100; ...}` Probably better because of floating point errors (when you add a lot of non-interger numbers)	[reply] [d/l] [select]