# [LON-CAPA-users] Extracting the numerical value from a solve()Maxima command

Seema Ali sali at vsb.bc.ca
Sat Jan 28 11:32:00 EST 2012

```It is a little messy, I'm still in construction/learning phase. =]

<problem>
<script type="loncapa/perl">\$base1 = &random(2,9,1);

do{
\$base2 = &random(2,9,1);
}while(\$base1==\$base2);

\$a = &random(2,3,1);
\$b = &random(4,7,1) * -1;
\$c = &random(1,10,1);

\$index = &random(1,2,1);
\$leftright = &choose(\$index,'left','right');

if(\$leftright=='right')
{
\$power1 = "\$a x";
\$power2 = "\$b x - \$c";

\$power1maxima = "\$a * x";
\$power2maxima = "\$b * x - \$c";
}
else
{
\$power1 = "\$a x + \$c";
\$power2 = "\$b x";

\$power1maxima = "\$a * x + \$c";
\$power2maxima = "\$b * x";
}

\$equation = "(\$power1maxima)*log(\$base1) = (\$power2maxima)*log(\$base2)";

\$solution = &cas('maxima',"float(solve((\$power1maxima)*log(\$base1) = (\$power2maxima)*log(\$base2),x))");
#\$solution =~ /(-?\d+(?:\.\d+)?)/;
\$solution =~ /(-?\d+?(?:\.\d+)?)/;
\$answer = \$1;</script><startouttext />Solve for <m>\$x\$</m> to the nearest hundredth where <m eval='on'>\$base1^{\$power1} = \$base2^{\$power2}</m>

<responseparam name="tol" type="tolerance" description="Numerical Tolerance" default="0.0001" />

</numericalresponse>
</problem>

-----Original Message-----
From: lon-capa-users-bounces at mail.lon-capa.org on behalf of Gerd Kortemeyer
Sent: Fri 1/27/2012 4:41 PM
To: Discussion list for LON-CAPA users
Subject: Re: [LON-CAPA-users] Extracting the numerical value from a solve()Maxima command

Hi,

Could you please send me the XML source code for your problem?

Thanks,

- Gerd.

On Jan 27, 2012, at 6:14 PM, Seema Ali wrote:

> Hi,
>
> This was my attempt to get Maxima to solve the following equation:
> \$base1^\$power1maxima = \$base2^\$power2maxima
> where \$power1maxima and \$power2maxima are linear equations and
> \$base1 and \$base2 are constant values.
>
> Below is a snippet of part of my code:
>
> \$solution = &cas('maxima',"float(solve((\$power1maxima)*log(\$base1) = (\$power2maxima)*log(\$base2),x))");
> \$solution =~ /(-?\d+(?:\.\d+)?)/;
>
>
> Here are a couple of examples of some values:
>
> Example 1:
> An equation it is trying to solve: (2 * x)*log(7) = (-7 * x - 7)*log(9)
> \$solution is [x = -.7980624185332027]
>
> Example 2:
> An equation it is trying to solve: (2x)log(4)=(?5x?8)log(3)
> \$solution is [x=?1063303930517583]
>
> The answer for Example 2 should be -1.063303930517583.  If I double click on the values on the page I get the decimal point, otherwise if I highlight them which is what I did for Example 2, the decimal is missing, which is a separate issue.
>
> Example 2 also generates this error:
> ERROR: Computer's answer is incorrect ("-1.063303930517583"). It is likely that the tolerance range [-1.06340393051758, -1.06320393051758] needs to be adjusted.
> This error occurred while processing response 1_7 in part 0
>
> My tolerance range is 5%.
>
> I think it is my attempt at a regular expression is probably causing this problem.
>
> How do I extract the numerical value from a solve command in Maxima?
>
>
> Thanks.
>
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> LON-CAPA-users at mail.lon-capa.org
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