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

Justin Gray jgray at math.sfu.ca
Thu Nov 21 14:27:43 EST 2019

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

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

On Thu, Nov 21, 2019 at 11:14 AM H. K. Ng <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> 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:
>>
>>
>>
>> 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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>> LON-CAPA-users at mail.lon-capa.org
>>
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>>
>
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