On Sat, 29 Mar 2014, Gerd Kortemeyer wrote:
Date: Sat, 29 Mar 2014 11:59:48 -0400
From: Gerd Kortemeyer <ko...@lite.msu.edu>
To: Itay Furman <it...@nospammail.net>,
Discussion list for LON-CAPA users <lon-capa-users@mail.lon-capa.org>
Subject: Re: [LON-CAPA-users] Does formula response support inequalities?
Hi,
On Mar 29, 2014, at 11:37 AM, Itay Furman <it...@nospammail.net> wrote:
Consider a certain physical in which stable equilibrium exists if
2*k*l^2 - mgL > 0,
where k,l,m,g, and L, are parameters.
I would like to challenge my students with a problem for which the
answer would be the above symbolic inequality.
However, as I understand I _cannot_ use formula response for that purpose; is
this correct? or did I miss something?
[snip]
No, formularesponse will not do this. But you can use customresponse or
mathresponse.
With mathresponse, you can do whatever you like with the student expression
inside of MAXIMA CAS.
With customresponse, you can do whatever you like with the student expression
inside of a Perl environment. From there, you can call MAXIMA if needed using
&cas(‘maxima’,…).
You probably want to accept “2*k*l^2>m*g*L” as correct, so I would in
customresponse:
Thank you for the detailed response.
This is exactly what I wished for.
I am impressed by the breadth and flexibility of the Lon-Capa system.
Best regards,
Itay
<problem>
<startouttext />
In which case do you have stable equilibrium?
<endouttext />
<customresponse answerdisplay="2*k*l^2 - m*g*L > 0">
<answer type="loncapa/perl"># Get left and right side of (in)equality
($left,$sign,$right)=($submission=~/^(.*)([\>\<\=])(.*)$/);
# If it's not an (in)equality, forget it
unless ($sign) { return 'BAD_FORMULA'; }
# If it's an equality, it's wrong
if ($sign eq '=') { return 'INCORRECT'; }
# If it's "smaller than", invert
if ($sign eq '<') { $inter=$left; $left=$right; $right=$inter; }
# Okay, so now we have $left>$right
# And compare to the expression we want
my $diff=&cas('maxima',"$left-($right)-(2*k*l^2-m*g*L)");
if ($diff=~/^Error/) { return 'BAD_FORMULA'; }
if ($diff==0) { return 'EXACT_ANS'; }
return 'INCORRECT';</answer>
<textline readonly="no" spellcheck="none" />
</customresponse>
</problem>
- Gerd.
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