Hello,
thanks for the prompt answer...
going down to business..
> First of all, you should know that the solve/linsolve routines do not
> take advantage of the "assume" database, so for example they will look
> for solutions where DX=0.
>
Well, yes. I tried so much to understand what was the problem that
I even tried the assume command, after I forgot to remove it from
the .max file.
> Interesting. In my Maxima (5.9.0 GCL 2.5.0 W2k), solve returns a
> solution, but the solution is incorrect (only correct if DY=0 or
> DX=coeff_y). The solution *is* correct, however, if I include the
> parameters among the variables to solve for. Perhaps that is an
> acceptable workaround for you?
The program I am writing attempts work on the interpolation/derivation
of a function on a structured grid, without restrictions: can
work on 1D, 2D or 3D, with uniform grid, power stretching or
generic grid.
I look for the coefficients of the desired discretized formula
solving a linear system: this system can
be rather convolute, as when the grid is generic and I would
like to have parameters something like x_d[0], x_d[1], x_d[2],
y_d[0],y_d[-1] etc.
As you see, using solve on all the parameters involved in place of
linsolve on the real unknowns of the problem would become
rather messy (at least I think) in analyzing the results to implement
and test, especially when the number of unknown increases, not
to mention that this is the only case found until now that does not
work, and I tested so many of them...
So, I would not want to implement a complex set of
parachute calls to just catch a limited number of
annoying exceptions.
In this respect, your suggestion is not easy to adopt as
workaround, but at least I am relieved to see that this
is a real issue, and not a figment of my imagination!
Best Regards
Raimondo Giammanco