[LON-CAPA-users] Forcing students to submit valid expressions for formula responses.

Justin Gray jgray at math.sfu.ca
Mon Oct 21 14:05:58 EDT 2013

The timeout errors that you are observing might be addressed by a recent
bug fix (see http://bugs.lon-capa.org/show_bug.cgi?id=6653) which I believe
will be available in LON-CAPA 2.11.

As long as there is no timeout, students should receive the feedback
"Unable to understand formula" with no tries counted if they submit an
expression with unbalanced parentheses.

Indeed, students often have difficulty using a linear syntax to express
their answers, with all the parentheses required to indicate the correct
order of operations. If the DragMath editor is turned on, students can use
it to preview their answers after typing them, even if they did not use the
editor to build the expression in the first place. If they do this, it
should become apparent that an expression like 2^-1/2 may not be what they
had intended. Here are a couple things that I have tried when I anticipate
that students may have some difficulty with syntax:

1) Add a comment next to the pencil icon "<startouttext
/>"<m>$\leftarrow$</m> Use the formula editor to preview your answers
before submitting."<endouttext />

2) Include an adaptive hint in the problem where you expect that many
students will violate proper syntax: "You submitted <m>$\text{2^-1/2} =
\displaystyle \frac{2^{-1}}{2}.$</m> If your answer is <m>$2^{-1/2}$</m>,
enter this as 2^(-1/2)." These hints can also be safely added to a live
problem within your course for syntax errors that you did not anticipate.


Justin Gray | Senior Lecturer
Department of Mathematics | Simon Fraser University
8888 University Drive, Burnaby | V5A 1S6 | Canada
Tel: +1 778.782.4237

On Mon, Oct 21, 2013 at 8:13 AM, Gerd Kortemeyer <korte at lite.msu.edu> wrote:

> Hi,
> On Oct 21, 2013, at 10:23 AM, Angus Findlay <afindlay at mta.ca> wrote:
> > When I give students formula response questions some of them don’t
> submit valid mathematic expressions. The most common problems are:
> >
> > 1) Not having balanced brackets. (i.e. number of left brackets do not
> match number of right brackets)
> > 2) Including invalid characters, such as quotation signs.
> > 3) Not including brackets, when necessary. (eg. 2^-1/2 instead of
> 2^(-1/2))
> >
> > I want to tell them that the expression is invalid, tell them why, and
> allow them to enter it again, without penalty. (Right now my LON-CAPA
> server times out on them, and asks them to try again later.)
> >
> > Is there a piece of standard code I can use for this, or if not, what it
> the easiest to implement a solution to this?
> You can use <customresponse> (available now) and intercept the answer
> before passing it on to the symbolic algebra system, or you can use the
> pre-processor before the formulas are passed on to the regular
> <mathresponse> or <formularesponse> - but I am not sure if the pre-process
> argument is in 2.10.1, and whether or not it will be in 2.11.
> I have no prefabricated piece of code on hand. I continue to be puzzled by
> the students' inability to produce valid expressions - it seems like there
> are very few rules, and they presumably used those $@$!$# graphing
> calculators for years …
> - Gerd.
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