On Feb 12, 2:22 pm, Volker Braun <vbraun.n...@gmail.com> wrote:
> You can also use the symbolic ring:
>
> sage: var('x,y,z,A,B,k,i,j,m')
> (x, y, z, A, B, k, i, j, m)
> sage: solve([x == A*i + B*j, y == A*k + B*m, z == B*(j-m) + A*(i-k)],
> [z,i,m])
> [[z == x - y, i == -(B*j - x)/A, m == -(A*k - y)/B]]
Yes, that works but the original poster was correct in pointing out
that there is some guesswork involved in choosing [z,i,m] as
"variables" (in another post) in order to find a relation between
x,y,z. By "solving" for [z,i,m], the other symbols A,B,k,j,x,y are
simply given no weight and are even considered invertible.I guess one could do solve([x == A*i + B*j, y == A*k + B*m, z == B*(j- m) + A*(i-k)],[z,A,B,k,i,j,m]) (i.e., all variables *except* the ones you want in your answer) in which case only x,y are not considered variables, so if z can be expressed solely in those, then that would constitute a "constant" value for z and hence will be reported. Indeed, that works for this example but it reports a lot of additional relations, because "solve" feels compelled to find suitable expressions for the other variables as well. Certainly a negative answer from solve should not be considered decisive (read the code! It's really just a bag of tricks applied until one succeeds) -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
