WeBWorK Problems

random(1,1,1) causing a hangup

random(1,1,1) causing a hangup

by Alex Jordan -
Number of replies: 1

On a 2.16 server, with seed 3163, I am experiencing an issue. I vaguely recall maybe some changes were made to random(), and maybe that is part of my issue.

I tried to minimize the code below to demonstrate the issue, but I can't seem to minimize it more than this. As it is, with seed 3163, the problem takes a long time to load and then reports an error. One way to clear it up is if I replace the "random(1,1,1)" with just "1".

The error message:
ERRORS from evaluating PG file: 
 'require' trapped by operation mask at /usr/lib/x86_64-linux-gnu/perl/5.26/Encode.pm line 5
   Died within Encode::Alias::find_alias called at line 114 of /usr/lib/x86_64-linux-gnu/perl/5.26/Encode.pm
   from within Encode::getEncoding called at line 132 of /usr/lib/x86_64-linux-gnu/perl/5.26/Encode.pm
   from within Encode::find_encoding called at line 166 of /usr/lib/x86_64-linux-gnu/perl/5.26/Encode.pm
   from within Encode::encode called at line 93 of [WW]/lib/Apache/WeBWorK.pm
   from within WeBWorK::PG::Local::alarm_handler called at line 34 of [PG]/lib/PGrandom.pm
   from within (eval) called at line 34 of [PG]/lib/PGrandom.pm
   from within PGrandom::mod called at line 46 of [PG]/lib/PGrandom.pm
   from within PGrandom::random called at line 1380 of [PG]/macros/PGbasicmacros.pl
   from within main::random called at line 33 of (eval 6114)
Compilation failed in require at /usr/lib/x86_64-linux-gnu/perl/5.26/Encode/Alias.pm line 22


The somewhat minimized problem code:
DOCUMENT();

loadMacros(
      "PGstandard.pl",
    );

##############################################

$a11 = random(1,1,1);
$a21 = random(0,0,1);
$a31 = random(0,0,1);
$a41 = random(1,9,1);

$a12 = random(1,5,1);
$a22 = random(-3,3,1);
$a32 = random(-5,2,1);
$a42 = random(-4,-2,1);

$a13 = $a21*$a32-$a31*$a22;
$a23 = $a31*$a12-$a11*$a32;
$a33 = $a11*$a22-$a21*$a12;
$a43 = random(-3,3,1);

$a14 = random(1,5,1);
$a24 = random(-3,3,1);
$a34 = random(-5,2,1);
$a44 = random(-4,-2,1);
 
while ($a11*($a22*$a33*$a44 + $a23*$a34*$a42 + $a24*$a32*$a43 - $a22*$a34*$a43 - $a23*$a32*$a44 - $a24*$a33*$a42) - $a41*($a12*$a23*$a34 + $a13*$a24*$a32 + $a14*$a22*$a33 - $a12*$a24*$a33 - $a13*$a22*$a34 - $a14*$a23*$a32) == 0)
{$a14 = random(1,5,1);
$a24 = random(-3,3,1);
$a34 = random(-5,2,1);
$a44 = random(-4,-2,1);}

ENDDOCUMENT();
In reply to Alex Jordan

Re: random(1,1,1) causing a hangup

by Danny Glin -

I don't think that random is the problem here.  When I create a problem with an infinite loop I get the same error message that you posted.  One tipoff is that the stack trace contains WeBWorK::PG::Local::alarm_handler, which is only invoked if processing a problem times out.

In previous versions of WeBWorK you would get a warning at the bottom of the page that suggested that there may be an infinite loop.  It looks like that warning isn't making it as far as the webpage anymore.

In fact, if you comment out the while loop, and display the values for all of the variables for that seed (3163), the matrix generated is

     1     4     0     1

     0     0     0     1

     0     0     0    -5

     7    -3    -3    -2

The first three columns of this matrix are linearly dependent, so rerandomizing the fourth column will never lead to a nonzero determinant.