LON-CAPA Help

Custom Response is a way to have a problem graded based on an algorithm. The use of this response type is generally discouraged, since the responses will not be analyzable by the LON-CAPA statistics tools.

For a single textfield, the student's answer will be in a variable $submission. If the Custom Response has multiple textfields, the answers will be in an array reference, and can be accessed as $$submission[0], $$submission[1], etc.

The student answer needs to be evaluated by Perl code inside the < answer > -tag. Custom Response needs to include an algorithm that determines and returns a standard LON-CAPA response. The most common LON-CAPA responses are:

EXACT_ANS: return if solved exactly correctly
APPROX_ANS: return if solved approximately
INCORRECT: return if not correct, uses up a try
ASSIGNED_SCORE: partial credit (also return the credit factor,
e.g. return(ASSIGNED_SCORE,0.3);)
SIG_FAIL, NO_UNIT, EXTRA_ANSWER, MISSING_ANSWER, BAD_FORMULA, WANTED_NUMERIC, WRONG_FORMAT: return if not correct for different reasons, does not use up a try

The answerdisplay is shown instead of the student response in 'show answer' mode after the answer date. The following example illustrates this:

<problem>
<startouttext />Accept an answer of around 90 or -90<endouttext />
  <customresponse answerdisplay="something near 90 or -90">
    <answer type="loncapa/perl">
# This examples uses perl 'regular expressions' for string evaluation. 
# Consult a perl reference for help understanding the regular expressions.
# We do not want a vector
if ($submission=~/\,/) { return 'EXTRA_ANSWER'; }
# Need a numerical answer here
if ($submission!~/^[\d\.\-\e]+$/i) { return 'WANTED_NUMERIC'; }
$difference=abs(90-abs($submission));
if ($difference==0) { return 'EXACT_ANS'; }
if ($difference < 0.1) { return 'APPROX_ANS'; }
return 'INCORRECT';</answer>
    <textline readonly="no" />
  </customresponse>
</problem>

Full list of possible return codes:

EXACT_ANS: student is exactly correct
APPROX_ANS: student is approximately correct
NO_RESPONSE: student submitted no response
MISSING_ANSWER: student submitted some but not all parts of a response
EXTRA_ANSWER: student submitted a vector of values when a scalar was expected
WANTED_NUMERIC: expected a numeric answer and didn't get one
SIG_FAIL: incorrect number of Significant Figures
UNIT_FAIL: incorrect unit
UNIT_NOTNEEDED: submitted a unit when one shouldn't
UNIT_INVALID_INSTRUCTOR: the unit provided by the author of the problem is unparsable
UNIT_INVALID_STUDENT: the unit provided by the student is unparasable
UNIT_IRRECONCIBLE: the unit from the student and the instructor are of different types
NO_UNIT: needed a unit but none was submitted
BAD_FORMULA: syntax error in submitted formula
WRONG_FORMAT: student submission did not have the expected format
INCORRECT: answer was wrong
SUBMITTED: submission wasn't graded
DRAFT: submission only stored
MISORDERED_RANK: student submitted a poorly order rank response
ERROR: unable to get a grade
ASSIGNED_SCORE: partial credit; the customresponse needs to return the award followed by the partial credit factor
TOO_LONG: answer submission was deemed too long
INVALID_FILETYPE: student tried to upload a file that was of an extension that was not specifically allowed
EXCESS_FILESIZE: student uploaded file(s) with a combined size that exceeded the amount allowed
COMMA_FAIL: answer requires the use of comma grouping and it wasn't provided or was incorrect