# [LON-CAPA-users] Formula response won't recognize "pi"

Raeburn, Stuart raeburn at msu.edu
Thu Nov 21 13:26:31 EST 2019

Grigory,

If you do *not* include a samples attribute in the formularesponse tag, then maxima will be used to compare the submitted formula with the expected answer.   This became the default starting with LON-CAPA 2.4.0 (June 2007).

However, if you include sample points in the formularesponse item, and your answer includes pi, see the example here: help.loncapa.org/fom/cache/361.html which shows how to include pi as a "variable" in the sampling points.

For example, the following will grade as correct a submission of:
1/sqrt(4*pi^2*L*C)

<problem>
<script type="loncapa/perl">
$ans = "1/(2*pi*sqrt(L*C))"; </script> <startouttext /> <p>Enter <m>$ \frac{1}{\sqrt{4\cdot\pi^{2} \cdot L\cdot C}} $</m></p> <endouttext /> <formularesponse answer="$ans" samples="pi,L,C@$pi,.1,.1:$pi,100.,100.#1">
<responseparam name="tol" type="tolerance" default="0.00001" description="Numerical Tolerance" />
</formularesponse>
</problem>

Stuart Raeburn
________________________________________
From: LON-CAPA-users <lon-capa-users-bounces at mail.lon-capa.org> on behalf of SIMIN, GRIGORY <SIMIN at engr.sc.edu>
Sent: Thursday, November 21, 2019 11:03 AM
To: Discussion list for LON-CAPA users
Subject: [LON-CAPA-users] Formula response won't recognize "pi"

Hi all!

I've found a strange issue in some problems requiring formula response.

I have a simple question to enter the formula for the resonant frequency.

An example of correct answer is (in other variations the formula could be a bit more complex than this one)

1/(2*pi*sqrt(L*C))

The correct solution is checked by sampling L and C values.

When I am entering the answer, I can see that LON-CAPA recognizes it because it displays the formatted formula as I am entering it:

[cid:image003.jpg at 01D5A05B.449F5B20]

But when I press submit, I got the response:

“unable to understand formula”

By experimenting with this, I found that the issue happens because of “pi” being a part of the answer.

If pi is replaced with 3.141, everything would work.

But it feels weird asking students to enter 3.141 instead of pi; besides, I don’t even want to give them a hint that pi is a part of the answer.

Why is this happening? Apparently LON-CAPA knows what “pi” means because it displays it correctly.

Thanks!

Grigory

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