[LON-CAPA-users] formula response question

[Peter Riegler]

Hi,

I have tested your code on my 2.8 server:
The problem is related to the +-2 in
$solution=7*exp(2*x)+-2*exp(-1*-7/4*x) .
So you should write
$solution="$M1*exp($d*x)+($M2)*exp(-1*$b/$a*x)
in your script. Note the parentheses around $M2.
I can't explain that to you perlwise because "...+-2*..." is legal perl.
As your script is written $M2 becomes negative very infrequently, hence 
you don't encounter such problems often.

Peter

James Mueller wrote:
> A student in a calculus course is entering an answer to a formula  
> response problem and keeps getting "Unable to understand formula" even  
> when they enter something simple like "x" for their answer.  The rest  
> of the students are reported to be not having troubles.  I assumed it  
> must be some problem with the script tat was triggered by the numbers  
> used for this particular problem.  After a quick look, I can't see  
> anything, but I have to admit my perl is rusty.  Anybody else se  anything?
> 
> The script is
> 
> <problem>
> <meta name="isbasedontime" content="1235265561" />
> <meta name="isbasedonres" content="\%2fres\%2fpitt\%2fathanas\%2fc2\ 
> %2ddiffeq\%2d21\%2eproblem" />
>     <script type="loncapa/perl">
> $b=0; $d=0; while($b==0 || $d==0){$b=&random(-10,10,1); 
> $d=&random(-10,10,1);}
> $a=-1*$b/$d; while($a==-1*$b/$d){$a=&random(1,10,1);}
> $c=&random(1,10,1); $i=&random(1,50,1);
> if($b<0){$s=" ";} if($b>0){$s="+";}
> $M1=$c/($a*$d+$b); $M2=$i-$M1;
> $solution="$M1*exp($d*x)+$M2*exp(-1*$b/$a*x) ";
>  </script>
>  <startouttext />
> <br />
> Determine the solution to the initial value differential equation <m  
> eval="on"> \[  $a y' $s $b y = $c e^{$d x} \hspace{.2in} y ( 0 )= $i  
> \]</m>
> <endouttext />
> 
> <p />
> <startouttext /><m>$ y ( x ) =  $</m><endouttext />
> <formularesponse samples="x@1:3#4" answer="$solution" id="11">
> <responseparam name="tol" default="0.001" type="tolerance"  
> description="Numerical Tolerance" />
>         <textline readonly="no" size="35" />
>     </formularesponse>
> </problem>
> 
> And the students variables for this problem are
> 
> %! 
> =(E2BIG=>0,EACCES=>0,EADDRINUSE=>0,EADDRNOTAVAIL=>0,EADV=>0,EAFNOSUPPORT 
> =>0,EAGAIN=>0,EALREADY=>0,EBADE=>0,EBADF=>0,EBADFD=>0,EBADMSG=>0,EBADR=> 
> 0,EBADRQC=>0,EBADSLT=>0,EBFONT=>0,EBUSY=>0,ECANCELED=>0,ECHILD=>0,ECHRNG 
> =>0,ECOMM=>0,ECONNABORTED=>0,ECONNREFUSED=>0,ECONNRESET=>0,EDEADLK=>0,ED 
> EADLOCK=>0,EDESTADDRREQ=>0,EDOM=>0,EDOTDOT=>0,EDQUOT=>0,EEXIST=>0,EFAULT 
> =>0,EFBIG=>0,EHOSTDOWN=>0,EHOSTUNREACH=>0,EIDRM=>0,EILSEQ=>0,EINPROGRESS 
> =>0,EINTR=>0,EINVAL=>0,EIO=>0,EISCONN=>0,EISDIR=>0,EISNAM=>0,EKEYEXPIRED 
> =>0,EKEYREJECTED=>0,EKEYREVOKED=>0,EL2HLT=>0,EL2NSYNC=>0,EL3HLT=>0,EL3RS 
> T=>0,ELIBACC=>0,ELIBBAD=>0,ELIBEXEC=>0,ELIBMAX=>0,ELIBSCN=>0,ELNRNG=>0,ELOOP=>0,EMEDIUMTYPE=>0,EMFILE=>0,EMLINK=>0,EMSGSIZE=>0,EMULTIHOP=>0,ENAMETOOLONG=>0,ENAVAIL=>0,ENETDOWN=>0,ENETRESET=>0,ENETUNREACH=>0,ENFILE=>0,ENOANO=>0,ENOBUFS=>0,ENOCSI=>0,ENODATA=>0,ENODEV=>0,ENOENT=>0,ENOEXEC=>0,ENOKEY=>0,ENOLCK=>0,ENOLINK=>0,ENOMEDIUM=>0,ENOMEM=>0,ENOMSG=>0,ENONET=>0,ENOPKG=>0,ENOPROTOOPT=>0,ENOSPC=>0,ENOSR=>0,ENOSTR=>0,ENOSYS=>0,ENOTBLK=>0,ENOTCONN=>0,ENOTDIR=>0,ENOTEMPTY=>0,ENOTNAM=>0,ENOTRECOVERABLE=>0,ENOTSOCK=>0,ENOTSUP=>0,ENOTTY=>0,ENOTUNIQ=>0,ENXIO=>0,EOPNOTSUPP=>0,EOVERFLOW=>0,EOWNERDEAD=>0,EPERM=>0,EPFNOSUPPORT=>0,EPIPE=>0,EPROTO=>0,EPROTONOSUPPORT=>0,EPROTOTYPE=>0,ERANGE=>0,EREMCHG=>0,EREMOTE=>0,EREMOTEIO=>0,ERESTART=>0,EROFS=>0,ESHUTDOWN=>0,ESOCKTNOSUPPORT=>0,ESPIPE=>0,ESRCH=>0,ESRMNT=>0,ESTALE=>0,ESTRPIPE=>0,ETIME=>0,ETIMEDOUT=>0,ETOOMANYREFS=>0,ETXTBSY=>0,EUCLEAN=>0,EUNATCH=>0,EUSERS=>0,EWOULDBLOCK=>0,EXDEV=>0,EXFULL=>0) 
> 
> $M1=7
> $M2=-2
> $a=4
> $b=-7
> $c=7
> $d=2
> $deg2rad=0.0174532925199433
> $i=5
> $pi=3.14159265358979
> $rad2deg=57.2957795130823
> $s=
> $solution=7*exp(2*x)+-2*exp(-1*-7/4*x)
> 
> 
> 
> 
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-- 
Peter Riegler
Fachhochschule Braunschweig/Wolfenbüttel
Salzdahlumer Str. 46/48, 38302 Wolfenbüttel
Tel. +49 5331 939 6314, Fax. +49 5331 939 6002
email: p.riegler@fh-wolfenbuettel.de
http://public.rz.fh-wolfenbuettel.de/~riegler