[LON-CAPA-users] Custom Response Division by Zero

[Josh Wolosz]

Hi Everyone,

I have a question in regards to Custom Response problems.  I would like to
try moving some of my labs into lon-capa, and one of the first ones
involves working with percent error (for high school freshman).

Here's what I would like to have happen:

1) Students enter an estimated value
2) Students enter the actual/measured value
3) Students then input their percent error which loncapa calculates and
determines if they are correct or not

Here is the script I have tried:

*<script type="loncapa/perl">
# Get the entered answer. First argument is partID, second is responseID
$given=&submission(1,11);
$example='You chose '.$given.' m';
$given2=&submission(3,4);
$example2='You chose '.$given2.' m';
$a=&abs($given2-$given)/$given2;
</script>*

I'm getting an error returned saying there is an illegal division by zero,
specifically:

*$a=&abs($given2-$given)/$given2;

*
I understand that at the beginning of the problem nothing has been
submitted, so $given2 has no value.  Is there a way around this?  Thanks
for your help, and I apologize if it is a very simple solution that I am
missing.

Sincerely
Joshua Wolosz

The full code is:

<problem>

    <parameter name="ordered" id="13" type="string_yesno" default="no"
description="Show Parts One-at-a-Time" />

<script type="loncapa/perl">
# Get the entered answer. First argument is partID, second is responseID
$given=&submission(1,11);
$example='You chose '.$given.' m';
$given2=&submission(3,4);
$example2='You chose '.$given2.' m';
$a1=100*&abs($given2-$given)/$given2;
</script>

<part id="1">
<startouttext />
<i><b>Note:</b> You do not need to include the units when you input your
calculations.</i><br></br>

What did you estimate the width of the object to be?
<endouttext />
<customresponse answerdisplay="$example" id="11">
    <answer type="loncapa/perl"># We do not want a vector
if ($submission=~/\,/) { return 'EXTRA_ANSWER'; }
# No units needed
if ($submission=~/^\d+\s+\w+$/) { return 'UNIT_NOTNEEDED'; }
# Need a numerical answer here
if ($submission!~/^[\d\.]+$/) { return 'WANTED_NUMERIC'; }
{ return 'EXACT_ANS'; }</answer>
    <textline readonly="no" />
</customresponse><startouttext />meters<endouttext />
</part>

<part id="3">
<startouttext />
What did you <u>measure</u> the width of the object to be?
<endouttext />
<customresponse answerdisplay="$example2" id="4">
    <answer type="loncapa/perl"># We do not want a vector
if ($submission=~/\,/) { return 'EXTRA_ANSWER'; }
# No units needed
if ($submission=~/^\d+\s+\w+$/) { return 'UNIT_NOTNEEDED'; }
# Need a numerical answer here
if ($submission!~/^[\d\.]+$/) { return 'WANTED_NUMERIC'; }
{ return 'EXACT_ANS'; }</answer>
    <textline readonly="no" />
</customresponse><startouttext />meters<endouttext />
</part>

<part id="5">
<startouttext />
What was your percent error for the width?
<endouttext />
<numericalresponse answer="$a1" id="194">
<responseparam name="tol" type="tolerance" default="0.5%"
description="Numerical Tolerance" />
    <textline readonly="no" />
</numericalresponse>
</part>
</problem

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