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

Gerd Kortemeyer korte at lite.msu.edu
Sun Jan 29 20:50:57 EST 2012

```Hi,

I think, as you suspected, it was just the regular expression. As the saying goes: "I have a problem. Hmmm, I know, I'll just use a regular expression! Now I have two problems …"

<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(-7,-4,1);
\$c = &random(1,10,1);

if (&random(0,1,1)) {
\$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";
}

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

\$solution<br />
<responseparam name="tol" type="tolerance" description="Numerical Tolerance" default="0.01" />

</numericalresponse>
</problem>

On Jan 28, 2012, at 11:32 AM, Seema Ali wrote:

> 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.
> >
> > _______________________________________________
> > LON-CAPA-users mailing list
> > LON-CAPA-users at mail.lon-capa.org
> > http://mail.lon-capa.org/mailman/listinfo/lon-capa-users
>
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>
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```