# [LON-CAPA-users] {Disarmed} RE: Formula response won't recognize "pi"

SIMIN, GRIGORY SIMIN at engr.sc.edu
Thu Nov 21 14:52:08 EST 2019

Justin,
Many thanks!
I will give it a try!
Grigory

From: LON-CAPA-users <lon-capa-users-bounces at mail.lon-capa.org> On Behalf Of Justin Gray
Sent: Thursday, November 21, 2019 2:28 PM
To: Discussion list for LON-CAPA users <lon-capa-users at mail.lon-capa.org>
Subject: Re: [LON-CAPA-users] Formula response won't recognize "pi"

You can evaluate the answer using Maxima and allow for a tolerance using mathresponse. In Maxima, the constant pi is written as %pi. Here is a possible coding for this problem, which will accept either %pi or a numerical approximation for pi:

<problem>
<script type="loncapa/perl">
$function = "1/sqrt(4*(%pi)^2*L*C)";$answer=&xmlparse('The correct answer is <m eval="on">$\frac{1}{\sqrt{4\cdot\pi^{2} \cdot L\cdot C}}$</m>');
</script>

<startouttext />
<p>Enter <m>$\frac{1}{\sqrt{4\cdot\pi^{2} \cdot L\cdot C}}$</m></p>
<endouttext />

<mathresponse answerdisplay="$answer" cas="maxima" args="$function">
</mathresponse>
</problem>

You will probably want to give students some instruction for formatting their answer.

Best,
Justin

--

Justin Gray
Senior Lecturer | Department of Mathematics
Simon Fraser University | SCK 10531
8888 University Dr., Burnaby, B.C. V5A 1S6
T: 778.782.4237

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On Thu, Nov 21, 2019 at 11:14 AM H. K. Ng <hkng at fsu.edu<mailto:hkng at fsu.edu>> wrote:
Hi,

Formularesponse using  cas with maxima works great.

<problem>
<script type="loncapa/perl">
$ansa = &cas('maxima','1/sqrt(4*pi^2*L*C)'); </script> <startouttext />What is formula for resonant frequency for an LC circuit? <endouttext /><br /> <startouttext /><m>$ \omega_{res} = $</m><endouttext /> <formularesponse answer="$ansa" id="12">
</formularesponse>

</problem>

Regards,
-hk

On Thu, Nov 21, 2019 at 11:05 AM SIMIN, GRIGORY <SIMIN at engr.sc.edu<mailto:SIMIN at engr.sc.edu>> wrote:

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:image001.jpg at 01D5A07B.3EF6C940]

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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