# [LON-CAPA-dev] Re: [LON-CAPA-users] exponent in formula response

Gerd Kortemeyer lon-capa-users@mail.lon-capa.org
Wed, 3 Feb 2010 07:52:48 -0500

Hi,

Yes, it was decided some time really early in the good old CAPA days that

2*10^4
2e4
2x10^4
2*10**4
2x10**4
2E4

are all ways to write the single number "2e4" - that's why is it currently so binding. While I don't really agree with having so many ways to write the same thing and the special coding it entails, I am worried that changing this now might cause damage in published problems.

While I have not tried it, I suspect that 1/2*10.0^4 would behave differently, since it does not exactly match any of the patterns above.

... legacy ....

- Gerd.

On Feb 3, 2010, at 4:26 AM, Peter Riegler wrote:

> Hi,
>
> one can find the reason for this in &implicit_multiplication in
> response.pm. There the multiplication operator in front auf a power of
> 10 is given very high binding power. Hence, the division in 1/2*10^4
> binds less than the multiplication. Hoever, in 1/2*19^4 division binds
> stronger than multiplication.
>
> I am posting this to dev as well as we might want to change this. To
> this end we would need to clarify why and if at all we need the
> currently implemented special behavior of the multiplication operator.
>
> Peter
>
>
>
> Todd Ruskell wrote:
>> James,
>> Not sure of a work-around, but I suspect I know *why* this is happening:
>> The expression 400/3*10^3 is ambiguous.   It appears your instructor
>> would like it to obey the apparent order of operations and evaluate to
>> 400/3*1000.  However, I believe the parser is interpreting this as
>> 400/(3*1000), or 400/3e3, which clearly puts the factor of 1000 in the
>> denominator.  That is, the parser is too smart for its own good, and
>> is treating 3*10^3 as a single number written in exponential notation.
>> One could argue over whether or not this is a "good thing"  but
>> changing the behavior of the parser at this time would undoubtedly
>> break many other "working" problems.   So the only fix I really see is
>> to make sure the students understand that although order of operations
>> is obeyed, a quantity like 6*10^3 is processed as a single
>> mathematical entity.
>> Todd
>> --
>> Todd Ruskell, Ph.D.                   Phone: 303-384-2080
>> Senior Lecturer in Physics          Fax:  303-273-3919
>> Golden, CO 80401
>> On Fri, Jan 29, 2010 at 11:35 AM, James Mueller <mueller@pitt.edu> wrote:
>>> A faculty member has a math problem that uses formula response with samples
>>> so that students can enter their final expression without having to plug it
>>> into a calculator.
>>>
>>> /res/athanas/c2-volume-1.problem
>>>
>>> an acceptable answer  (depending on the randomization) might be
>>> 3.14159*(400/3*19^3-80/4*19^4+4/5*19^5
>>>
>>> She has noticed an issue when the end-point of the integration is 10. A
>>> submission such as
>>> 3.14159*(400/3*10^3-80/4*10^4+4/5*10^5)
>>> is evaluated as incorrect, whereas if the student explicitly adds
>>> parenthesis,
>>> 3.14159*(400/3*(10^3)-80/4*(10^4)+4/5*(10^5))
>>> everything works as expected.
>>>
>>> So for 10, and only 10, there seems to be a problem.
>>>
>>> Any ideas as to How she might fix this problem?
>>> (other than the one I came up with,which is choose random numbers such that
>>> 10 is never the endpoint of the integration in x)
>>>
>>>
>>> <problem>
>>>   <script type="loncapa/perl">
>>> $n=1.123; while ($n !=&roundto($n,1) ){ >>>$a=&random(1,5,1); $b=&random(1,20,1);$n=$b/$a;}
>>> for ($x = 0;$x<=$n;$x+= 0.001) {
>>>    push @X1, $x; >>> push @Y1,$b*$x-$a*$x**2; } >>>$p=($a**2)/5*($n**5)-$a*$b/2*($n**4)+($b**2)/3*($n**3); >>>$pi=3.14159;
>>> $volume1="$pi*$p"; >>>$example=3.14159*(7**3/3+(7/2)**2-14*exp(2));
>>> </script>
>>> <startouttext />
>>> <br />
>>> Determine the volume of the solid formed by rotating about the
>>> <m>$x$</m>-axis, the region above the <m>$x$</m>-axis and below the curve <m
>>> eval="on">$\;\; y =$b x - $a x^2\,$</m>. <p />
>>> <endouttext />
>>> <gnuplot width="400" grid="on" align="center" font="medium" height="300"
>>> border="on" bgcolor="xffffff" fgcolor="x000000" alttag="dynamically
>>> generated plot" transparent="off">
>>>    <xlabel>x</xlabel>
>>>    <curve linestyle="lines" name="" color="x8B0000" pointtype="1"
>>> pointsize="1">
>>>        <data>@X1</data>
>>>        <data>@Y1</data>
>>>    </curve>
>>> </gnuplot>
>>> <p />
>>> <startouttext />Volume of the solid is
>>> <formularesponse answer="$volume1" samples="x@1:4#2" id="11"> >>> <responseparam name="tol" default="0.001" description="Numerical Tolerance" >>> type="tolerance" /> >>> <textline size="55" readonly="no" /> >>> </formularesponse> >>> <m> units$^3$.</m> >>> <br />Use <m>$\pi=3.14159$</m> and round your answer to 3 decimal places. >>> <br /> >>> You do not need to do calculations. For example <m eval="on">$example </m>
>>> can be given as  3.14159(7^3/3+(7/2)^2-14exp(2)). <endouttext />
>>> </problem>
>>>
>>> _______________________________________________
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>>> LON-CAPA-users@mail.lon-capa.org
>>> http://mail.lon-capa.org/mailman/listinfo/lon-capa-users
>>>
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>
> --
> Peter Riegler
> Fakultät Informatik
> Ostfalia Hochschule für angewandte Wissenschaften
> Fachhochschule Braunschweig/Wolfenbüttel
> Salzdahlumer Str. 46/48
> 38302 Wolfenbüttel
> Fon: ++49 5331 939 31540
> http://public.rz.fh-wolfenbuettel.de/~riegler
>
>
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