#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

    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

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

    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

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

    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

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

    • status: pending --> closed
     
  • SourceForge Robot

    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
    the administrator of this Tracker).

     

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