\label{Custom_Response_Problems}
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.

The student answer is stored in the
variable \$submission, and needs to be evaluated by Perl code inside the <answer>-tag. Custom Response needs to return a standard LON-CAPA. The most common response are:
\begin{itemize}
\item EXACT\_ANS: return if solved exactly correctly
\item APPROX\_ANS: return if solved approximately
\item INCORRECT: return if not correct, uses up a try
\item SIG\_FAIL, NO\_UNIT, EXTRA\_ANSWER, MISSING\_ANSWER, BAD\_FORMULA, 
WANTED\_NUMERIC: return if not correct for different reasons, does not use up a try
\end{itemize}
The answer display is shown instead of the student response in 'show answer' mode.
The following example illustrates this:
\begin{verbatim}
<problem>
<startouttext />Accept an answer of around 90 or -90<endouttext />
  <customresponse answerdisplay="something near 90 or -90">
    <answer type="loncapa/perl">
# 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>
\end{verbatim}


Full list of possible return codes:
\begin{itemize}
\item EXACT\_ANS: student is exactly correct
\item APPROX\_ANS:  student is approximately correct
\item NO\_RESPONSE: student submitted no response
\item MISSING\_ANSWER: student submitted some but not all parts of a response
\item EXTRA\_ANSWER: student submitted a vector of values when a scalar was expected
\item WANTED\_NUMERIC: expected a numeric answer and didn't get one
\item SIG\_FAIL: incorrect number of Significant Figures
\item UNIT\_FAIL: incorrect unit
\item UNIT\_NOTNEEDED: Submitted a unit when one shouldn't
\item UNIT\_INVALID\_INSTRUCTOR: the unit provided by the author of the problem is unparsable
\item UNIT\_INVALID\_STUDENT: the unit provided by the student is unparasable
\item UNIT\_IRRECONCIBLE: the unit from the student and the instructor are of different types
\item NO\_UNIT: needed a unit but none was submitted
\item BAD\_FORMULA: syntax error in submitted formula
\item INCORRECT: answer was wrong
\item SUBMITTED: submission wasn't graded
\item DRAFT: submission only stored
\item MISORDERED\_RANK: student submitted a poorly order rank response
\item ERROR: unable to get a grade
\item ASSIGNED\_SCORE: there is a resource.partid.responseid.awarded the real awarded should be set to the average of the individual awards
\item TOO\_LONG: answer submission to CAPA engine longer than 500 characters
\item INVALID\_FILETYPE: student tried to upload a file that was of an extension that was not specifically allowed 
\item COMMA\_FAIL: answer requires the use of comma grouping and it wasn't provided or was incorrect

\end{itemize}