On Aug 19, 11:06 pm, Robert Bradshaw <rober...@math.washington.edu>
wrote:
> On Wed, 19 Aug 2009, KvS wrote:
>
> > Dear all,
>
> > just started exploring Sage (via sagenb.org), I'm very enthousiastic
> > about the concept and am very eager to leave 'black box' Mathematica
> > asap. One issue however I can't seem to get my head around, namely
> > what exactly is the 'right' way to think of and work with Sage-
> > functions (as opposed to function constructs in the Python language)?
>
> > E.g. when trying to plot a piecewise function, this works:
>
> > f1 = lambda x:x
> > f2 = lambda x:x^2
> > f = Piecewise([[(0,1),f1],[(1,2),f2]])
> > P = f.plot()
>
> > whereas this (and several modifications of it I tried):
>
> > x=var('x')
> > f1(x)=x
> > f2(x)=x^2
> > f(x)=Piecewise([[(0,1),f1(x)],[(1,2),f2(x)]])
> > P=f.plot()
>
> > throws a TypeError:
>
> > File "ring.pyx", line 272, in
> > sage.symbolic.ring.SymbolicRing._element_constructor_ (sage/symbolic/
> > ring.cpp:4456)
> > TypeError
>
> > Personally I would prefer the second approach as I would like to use
> > only Sage-functions for mathematical functions (so not use lambda:
> > etc.) to keep a notion of distinction between the mathematical objects
> > on the one hand and the Python code on the other hand that controls
> > the program flow. But it seems that I just don't really understand how
> > to do that. Why is the second piece of code wrong and what would be
> > the 'right' way to do it? Is there a function construct in Sage like
> > the concept of a 'pure function' in Mathematica, so something like
> > f=Function(x,x^2), where x is only a dummy that has no link with any x
> > that might be defined before this command?
>
> > Many thanks in advance for your time.
>
> Probably what you want to do is
>
> sage: f(x) = x^2
>
> Note that piecewise functions have a lot of rough edges, so are probably
> not the best examples for "how things should work."
>
> - Robert
You mean this should be the 'right' way to define a Sage-function?
Don't you need x=var('x') as well? And how would you define a Sage-
function inside a Python class then, this:
class Test:
def __init__():
x=var('x')
self.func(x)=sin(x)
t=Test()
yields a syntax error?
(Sorry for all the questions...)
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