Re: [Axiom-math] if-expression and variables

[Stefan Karrmann]

Dear all,

thanks for your answers. They clears a lot.

I actually want to integrate test1 and solve an differential equation
with it.

E.g.
test2 x == rho * test1 x
y = operator 'y
odeq := D(y x) = test2 x
solve(odeq, y, x)

Obviously, the solution is "formally"

y_sol x == integrate(test2 x,x)

Kind regards,
Stefan

Am Dienstag, den 03.05.2011, 11:21 +0200 schrieb Ralf Hemmecke:
> Dear Stefan,
> 
> as others already have pointed out, for Axiom, your question is not 
> really well posed.
> 
> In Axiom
> 
>    if x<10 then 2*x else 5*x^2
> 
> is *not* an expression (as you might know it from other untyped CAS like 
> Mathematica or Maple), but rather a programming language construct. In 
> other words, if Axiom sees this, it is evaluated. So the result is 
> either 2*x or 5*x^2 depending on the (boolean) outcome of the evaluation 
> of x<10.
> 
> I think, Bill suggested to use something like InputForm. There it would 
> be possible to represent an if-expression unevaluated.
> 
> But you should rather say what you actually want (it's not the same what 
> you expect).
> 
> In order for us to suggest you a proper way to handle your use case, you 
> should tell us why you want a piecewise function and (more important) 
> what you later want to do with that function.
> 
> Until we have that information, everything would be just digging in the 
> dark.
> 
> Ralf
> 
> On 04/30/2011 08:40 PM, Stefan Karrmann wrote:
> > Dear all,
> >
> > I'm new to axiom and have a problem with piecewise functions.
> >
> > test1 (x | x<  10) == 2*x
> > test1 (x | x >= 10) == 5*x^2
> > [was typo: test1 (x | x<  10) == 5*x^2]
> > test1
> > ->
> >     test1 (x | x<  10) == 2x
> >     test1 (x | ^ x<  10) == 5x
> >                                                     Type: FunctionCalled
> > test1 y
> > ->
> >       2
> >     5y
> >
> > I expected something like (if y<  10 then 2*y else 5*y**2).
> >
> > How is it possible to pass a Variable to a piecewise function respecting
> > the pieces?
> >
> > PS: Using a block and =>  or explicit if-then-else does not help.