## WeBWorK Problems

### Debugging a (simple?) product rule question - answer submission not working right ### Debugging a (simple?) product rule question - answer submission not working right

by Sean Fitzpatrick -
Number of replies: 5

We have a (non-OPL) problem on the product rule, which seems simple enough, but something is not working correctly.

If I try submitting an answer, it gets marked as correct or incorrect, but the message doesn't show up in the results table: I haven't been able to reproduce it, but one of my students reported the following error:

DBD::mysql::st execute failed: Data too long for column 'frozen_hash' at row 1 at /opt/webwork/webwork2/lib/WeBWorK/DB/Schema/NewSQL/Std.pm line 837.
Here is the code for the problem:

## DESCRIPTION

## This is Problem 2.4.15 from the APEX Calculus text. It covers differentiation of basic trig functions and the product rule.

## ENDDESCRIPTION

## DBsubject(Calculus - single variable)

## DBchapter(Differentiation)

## DBsection(Product rule (with trigonometric functions))

## Level(2)

## Institution('Valdosta State University')

## Author('S. V. Ault')

## RevisedBy('F. J. Francis')

## TitleText1('APEX Calculus')

## AuthorText1('Hartman')

## EditionText1('3.0')

## Section1('2.4')

## Problem1('15')

## MO(1)

## Keywords('derivative', 'product rule', 'trig functions', 'ULETH-MATH1560', 'ULETH-MATH1565')

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

#  Initialization

DOCUMENT();

# Load whatever macros you need for the problem

# REQUIRED: Used for basic question and answer operations.

"PGstandard.pl",

# REQUIRED: Used for expression parsing.

"MathObjects.pl",

# Usually required for proper text formatting.

"PGML.pl",

# Used to provide contextual help for how to type inequalities/intervals.

);

# Sets up basic problem information.

TEXT(beginproblem());

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

#   Setup

#-ULETH-#

Context("Numeric");

$a = random(2,9,1);$f = Formula("x^{$a}");$fp = $f->D('x');$r = random(1,2,1);

if ($r==1) {$g = Formula("sin(x)");

$gp = Formula("cos(x)");$ans = Formula("$f*cos(x) +$fp*sin(x)")->reduce();

} else {

$g = Formula("cos(x)");$gp = Formula("-sin(x)");

$ans = Formula("-$f*sin(x) + $fp*cos(x)")->reduce(); }$fb = Formula($f*$gp)->reduce();

$gb = Formula($fp*$g)->reduce(); #-ENDULETH-# ############################# # Problem Text #-ULETH-# BEGIN_PGML Compute the derivative of the given function. >>[f(x) = [$f*$g].]<< [f'(x) = ] [_______________] [@ AnswerFormatHelp("formulas") @]* END_PGML #-ENDULETH-# ############################# # Solution #-ULETH-# BEGIN_PGML_SOLUTION Use the Product Rule. [ f'(x) = ([$f])([$gp]) + ([$fp])([$g]) = [$fb] + [$gb] = [$ans].

]

END_PGML_SOLUTION

#-ENDULETH-#

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

#-ULETH-#

# Setting this to 1 means that students will receive feedback on whether their

# answers are correct.

$showPartialCorrectAnswers = 0; #-ENDULETH# ANS($ans->cmp() );

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

COMMENT('

Randomization provides 16 different possible versions of this question.<BR>

Includes a solution set.<BR>

Made from a ULETH template.<BR>

');

ENDDOCUMENT(); In reply to Sean Fitzpatrick

### Re: Debugging a (simple?) product rule question - answer submission not working right

by Glenn Rice -
The reason the message doesn't show up is because you have \$showPartialCorrectAnswers set to 0.

I am not sure where the error comes from. In reply to Sean Fitzpatrick

### Re: Debugging a (simple?) product rule question - answer submission not working right

by Danny Glin -

The only tables that have a 'frozen_hash' column have to do with achievements.

I don't know anything about achievements, so I have a couple of wild guesses as to what's causing that error.  The default max size for the frozen_hash column is 1024 characters, so based on the error WW is trying to store something longer than that in the column.  My guesses are:

1. There is too much information to fit into 1024 characters, which could be because there are a lot of assignments/achievements in the course.
2. The hashing algorithm is doing something WW doesn't expect, which is causing the hash to be longer.  This could be because of a change to a different character set (e.g. utf8). In reply to Danny Glin

### Re: Debugging a (simple?) product rule question - answer submission not working right

by Sean Fitzpatrick -

Ahh, thanks.

I do have achievements turned on. (Haven't used them in the past but I saw Alex's video and they looked like fun.)

So far only one student complaining so I won't worry too much. In reply to Sean Fitzpatrick

### Re: Debugging a (simple?) product rule question - answer submission not working right

by Sean Fitzpatrick -
Spoke too soon. Just got another email from a student with the error, but on a different problem. Probably there's one misbehaving achievement badge? I'm not sure the error gives me enough to track that down. Or maybe I just need to cut down on the number of achievements available. (I assigned them all since that seemed simpler.)

This student gave a bit more detail on the error:   In reply to Sean Fitzpatrick

### Re: Debugging a (simple?) product rule question - answer submission not working right

by Andras Balogh -

I get the same error message for questions with many entries (8x6 matrix (48 entries)) AND with achievements enabled AND for incorrect answers. For smaller matrices or with achievements deleted or with correct answer there is no error message.