#556 solve confused by ratvars

open
nobody
5
2006-09-09
2004-04-09
No

solve(rat(a+c,a,b,c,d),[a,b])
=> [[a=-%r1, b=%r1]] NO!

Remove the extra variable:

solve(rat(a+c,a,b,c),[a,b])
=> [[a = - c, b = %r2]] OK

Also works fine if you call algsys directly:

algsys([rat(a+c,a,b,c,d)],[a,b]);

At first I thought this had something to do with the
variable *ordering* in the first case, but in fact it
happens with all orderings. The problem is the number
of ratvars.

Note that this is *not* an artificial situation. It is
common to have CREs with more ratvars than they use
after arithmetic operations, e.g. rat(a+b)-rat(a).

Discussion

  • Robert Dodier

    Robert Dodier - 2006-07-29
    • labels: --> 460522
     
  • Robert Dodier

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

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