## #759 solving E/exponent equation hangs

closed
nobody
5
2011-02-08
2005-06-23
Anonymous
No

I cancelled both of these after waiting several minutes:

(%i26) solve(2*%e^(-200*t)=8*%e^(-8000*t),t);

Maxima encountered a Lisp error:

Console interrupt.

Automatically continuing.
To reenable the Lisp debugger set *debugger-hook* to nil.
(%i27) solve(0=-2*%e^(-200*t)+8*%e^(-8000*t),t);

Maxima encountered a Lisp error:

Console interrupt.

Automatically continuing.
To reenable the Lisp debugger set *debugger-hook* to nil.

David Logan
djlogan2@comcast.net

## Discussion

• Barton Willis - 2005-07-02

Logged In: YES
user_id=895922

(%i1) 2*%e^(-200*t)=8*%e^(-8000*t)\$
A workaround:

2*%e^(-200*t)=8*%e^(-8000*t)\$
(%i2) ratsubst(z,exp(-200*t),%);
(%o2) 2*z=8*z^40
(%i3) solve(%,z);
(%o3)
[z=%e^((2*%i*%pi)/39)/4^(1/39),z=%e^((4*%i*%pi)/39)/4^(1/39),z=%e^((2*%i*%pi)/13)/4^(1/39),z=%e^((8*%i*%pi)/39)/4^(1/39),z=%e^((10*%i*%pi)/39)/4^(1/39),z=%e^((4*%i*%pi)/13)/4^(1/39),z=%e^((14*%i*%pi)/39)/4^(1/39),z=%e^((16*%i*%pi)/39)/4^(1/39),z=%e^((6*%i*%pi)/13)/4^(1/39),z=
<junk deleted>,z=0]

Barton

• Robert Dodier - 2006-08-12
• labels: --> 460522

• Robert Dodier - 2006-08-12

Logged In: YES
user_id=501686

Seems likely Maxima knows how to solve the problem -- namely
solve(2*%e^(-200*t)=8*%e^(-8000*t),t); -- but it is just
taking a long time. A similar problem with smaller
coefficients like solve(2*%e^(-2*t)=8*%e^(-80*t),t); yields
a messy solution after a second or two. Not sure whether to
consider the observed behavior a bug.

• Robert Dodier - 2006-09-09
• labels: 460522 --> Lisp Core - Solving equations

• Dieter Kaiser - 2011-01-25

I think, we should close this bug report as won't fix. Maxima is able to solve the type of equation. The reported example generates 7800 solutions. That is too much. But it is possible to formulate a workaround.
Dieter Kaiser

• Dieter Kaiser - 2011-01-25
• status: open --> pending

• SourceForge Robot - 2011-02-08
• status: pending --> closed

• SourceForge Robot - 2011-02-08

This Tracker item was closed automatically by the system. It was
previously set to a Pending status, and the original submitter
did not respond within 14 days (the time period specified by