#670 SOLVE gives a wrong answer

open
nobody
5
2006-09-09
2005-01-19
Anonymous
No

When I try this:

kill(all)$
x(t):=exp(t)*cos(t)$
y(t):=exp(t)*sin(t)$
z(t):=exp(t)*sqrt(3)$
g(t):=[x(t),y(t),z(t)]$
d(t):=sqrt(g(t).g(t))$
d(t)=2;
solve(%,t);

I get the following output:
[t=log(-2/sqrt(3)),t=log(2/sqrt(3))]
but the correct answer should be t= 0.
Using TRIGSIMP or TRIGREDUCE I get te correct answer:

trigreduce(d(t)=2);
solve(%,t);

Now I get:
[t = 0]

Is this a bug?

Franco Buratti (Italy)
bufranz@hotmail.com

---------------------------------------------
Maxima version: 5.9.1
Maxima build date: 7:34 9/24/2004
host type: i686-pc-mingw32
lisp-implementation-type: Kyoto Common Lisp
lisp-implementation-version: GCL 2.6.5
---------------------------------------------

Discussion

  • Barton Willis
    Barton Willis
    2005-03-05

    Logged In: YES
    user_id=895922

    Yes, this is a bug. Another solution is t = %i * %pi.
    Maxima misses that solution after applying trigreduce.

    Barton

     
  • Robert Dodier
    Robert Dodier
    2006-08-04

    • labels: --> 460522
     
  • Robert Dodier
    Robert Dodier
    2006-08-04

    Logged In: YES
    user_id=501686

    Observed in 5.9.3cvs.

     
  • Robert Dodier
    Robert Dodier
    2006-09-09

    • labels: 460522 --> Lisp Core - Solving equations