In
Problem setLinearAlgebra17DotProductRn/ur_la_17_13.pg
with initial seed 773, one gets the following error. Other seeds work
fine and the code looks fine so I'm really confused. The error seems to
be coming from a sqrt error in line 31 of the code. I initially thought
the sqrts later in the problem were causing the error but even when
inserted code to insure that those numbers $norm_x, $norm_y were
positive, the problem still didn't work as the error was coming
earlier. But there's no square root earlier!
I'm baffled.
Tom Software Error
WeBWorK has encountered a software error while attempting to process this problem. It is likely that there is an error in the problem itself. If you are a student, contact your professor to have the error corrected. If you are a professor, please consut the error output below for more informaiton. Error messages
Can't take sqrt of 4.44089e16 at (eval 1491073) line 31. Error context
Problem1 ERROR caught by Translator while processing problem file:setHagedorn/WeirdError.pg * Can't take sqrt of 4.44089e16 at (eval 1491073) line 31.
*
Input Read 1 ##DESCRIPTION 2 ##KEYWORDS('linear algebra', 'inner product', 'dot product', 'angle') 3 ## 4 ##ENDDESCRIPTION 5 6 DOCUMENT(); # This should be the first executable line in the problem. 7 8 loadMacros( 9 PG.pl, 10 PGbasicmacros.pl, 11 PGchoicemacros.pl, 12 PGanswermacros.pl, 13 PGgraphmacros.pl, 14 PGnumericalmacros.pl, 15 PGstatisticsmacros.pl, 16 PGauxiliaryFunctions.pl, 17 PGmatrixmacros.pl 18 ); 19 20 TEXT(beginproblem()); 21 $showPartialCorrectAnswers = 1; 22 23 $prod = 0; 24 $norm_x = 0; 25 $norm_y = 0; 26 27 foreach $i (0..1) { 28 $x[$i] = non_zero_random(5,5,1); 29 $y[$i] = non_zero_random(5,5,1); 30 if ($y[$i] == $x[$i]) { 31 $y[$i] = 6; 32 } 33 $prod = $prod + $x[$i] * $y[$i]; 34 $norm_x = $norm_x + $x[$i] * $x[$i]; 35 $norm_y = $norm_y + $y[$i] * $y[$i]; 36 37 } 38 39 if($norm_x <0){$norm_x= $norm_x}; 40 if($norm_y <0){$norm_y= $norm_y}; 41 42 $norm_x = sqrt($norm_x); 43 $norm_y = sqrt($norm_y); 44 45 $angle = arccos( $prod / $norm_x / $norm_y); 46 47 BEGIN_TEXT 48 49 Find the angle ( alpha ) between the vectors 50 { mbox( display_matrix([[$x[0]], [$x[1]]]), ' and ', display_matrix([[$y[0]], [$y[1]]]), '.' ) } 51 $BR 52 ( alpha = ) {ans_rule(20)}. 53 54 END_TEXT 55 56 ANS(num_cmp($angle)); 57 ANS($norm_x); 58 ANS($norm_y); 59 ANS($x[1]); 60 ANS($x[0]); 61 ANS($y[0]); 62 ANS($y[1]); 63 64 65 ENDDOCUMENT(); # This should be the last executable line in the problem.

Edit this problem
This set is visible to students.
< Post or View Comments >
