"Oguz Bayrak" asked:
> I have 16 equations and I want to substitude them into another 6
> equations.I would realy be pleased if you can help me with an idea or
> with a source code or a demo.
>
This question is still not answered - perhaps because it is not
very precisely posed.
To perform multiple substitutions at a time, you may wish to
consider the function SUBLIS. For substitution of one
expression you can also use SUBST or the more powerful
RATSUBST, which is sometimes quite time consuming.
The crucial question is in what form you have the 16
equations. Substitution is easy if these 16 equations are
explicit in 16 variables that you use in the 6 equations that
you wish to transform by a substitution.
sublis ([x=16*sin(t), y=8*cos(t)], z*x = (t*y)^2);
Here you have a list of two equations that are explicit in
the variables that you want to replace in one given expression.
That is easy, and it works also when the second argument
of SUBLIS is a list of equations.
(A list is also an expression, so it has to work!)
If you cannot isolate the variables that you want to replace in
your six equations, the situation is *much* more difficult -
I think you should then try to use SCSIMP
(do example(scsimp) for a short demo),
Simplification with constraints is sometimes done with
Groebner bases, but we do not currently have a good
package to compute groeber bases.
If this does not help, I think you should tell us more about your
problem.
Greetings, Boris