On Wed, 19 Aug 2009, KvS wrote:
>
>
>
> 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?
It's just syntactic sugar.
> 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?
>
Do (x^3-x).function(x)
See x.function? for more documentation (where x here is a
variable/expression).
- Robert
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to sage-support@googlegroups.com
To unsubscribe from this group, send email to
sage-support-unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sage-support
URLs: http://www.sagemath.org
-~----------~----~----~----~------~----~------~--~---
