Can you suggest concise language that would clarify this? Even for someone
as sophisticated as you, apparently my language ("Solve only gives
solutions valid for *all* values of parameters (as opposed to variables)")
wasn't clear enough.
-s
On Wed, Jun 12, 2013 at 1:01 PM, Henry Baker <hbaker1 at pipeline.com> wrote:
> Thanks, Stavros, for putting up with my density!
>
> I get it now.
>
> However, the documentation on 'solve', 'linsolve', etc., need to be fixed
> to document this behavior.
>
> I just did '? solve', and the documentation said nothing about this issue.
>
> At 09:52 AM 6/12/2013, Stavros Macrakis wrote:
> >Extraneous equations add parameters. As I said, solve gives solutions
> that are correct for all values of all parameters.
> >
> >Thus:
> >
> > solve([x=0],[x]) => [[x=0]]
> >
> >but
> >
> > solve([x=0,y=2],[x]) => []
> >
> >because there is no solution for all values of y, which is considered a
> parameter, since it is not listed as a variable.
> >
> >In your example, you have equations like h0 = g0 + f0 - e0 which are
> composed entirely of parameters.
> >
> > -s
> >
> >On Wed, Jun 12, 2013 at 12:21 PM, Henry Baker <hbaker1 at pipeline.com>
> wrote:
> >Your comment doesn't appear to me to be relevant to the particular set of
> equations that I gave.
> >
> >The equations are all linear, and solve works fine without the extraneous
> equations:
> >
> >(%i22) eqn12;
> >(%o22) [d0 = c0 + b0, d1 = c1 + b1, d2 = c2 + b2]
> >(%i23) d;
> >(%o23) [d0, d1, d2]
> >(%i24) solve(eqn12,d);
> >(%o24) [[d0 = c0 + b0, d1 = c1 + b1, d2 = c2 + b2]]
> >(%i25)
> >
> >How can the extraneous (linear) equations screw up solve?
> >
> >At 09:08 AM 6/12/2013, Stavros Macrakis wrote:
> >>Solve only gives solutions valid for all values of parameters (as
> opposed to variables). For example:
> >>
> >>(%i12) solve([x=a,x=-a],[x]); <<< no solutions for all a
> >>(%o12) []
> >>(%i13) solve([x=a,x=-a],[x,a]); <<< make a into a variable
> >>(%o13) [[x = 0, a = 0]]
> >>
> >>On Wed, Jun 12, 2013 at 11:38 AM, Henry Baker <hbaker1 at pipeline.com>
> wrote:
> >>Solve doesn't work, either!
> >>
> >>(%i7) d;
> >>(%o7) [d0, d1, d2]
> >>(%i8) eqns;
> >>(%o8) [d0 = c0 + b0, d1 = c1 + b1, d2 = c2 + b2, h0 = g0 + f0 - e0,
> >>h1 = g1 + f1 - e1, h2 = g2 + f2 - e2, f0 = e0 + b0, f1 = e1 + b1,
> >>f2 = e2 + b2, g0 = e0 + c0, g1 = e1 + c1, g2 = e2 + c2]
> >>(%i9) solve(eqns,d);
> >>(%o9) []
> >>(%i10)
>
>