On Jun 27, 3:22 pm, Michael Orlitzky <mich...@orlitzky.com> wrote:
> I'll take a simple example. I'd like to integrate (or differentiate, or
> whatever) the following function,
>
> x = var('x')
>
> a = x
> b = 2*x
Here you probably mean something else. Are you getting a deprecation
warning?
It's better to define
a(x) = x
b(x) = 2*x
in which case you don't need to define x as a variable, it will be
done for you. The difference is between function notation and
"symbolic expressions"; basically, one of them allows input nicely
because you said what the variable was, the other doesn't. The
canonical example is
f = x + y - y
f(2) = ???
I don't actually quite agree with this, but it's a design decision
that's been made that in this case it's not clear whether x or y was
the input. Doing
f(x) = x + y - y
makes it explicit (in accordance with Python style) that x is the
variable.
>
> def f(x):
> if (a(x) < b(x)):
in which case this would be fine
> return 0
> else:
> return 1
>
> in Python code. Is there a way to make functions like these behave
> symbolically?
The easiest way to do this is to make them a class inheriting from
BuiltinFunction. There are some very good examples in the functions/
folder.
I don't think that the Piecewise class can handle this sort of thing,
and in any case its capabilities are somewhat limited.
However, it might be nice to have something that was a wrapper
@symbolicfunction
def f(x):
return some_expression_in_x(x)
Others have ideas whether this is good/feasible?
- kcrisman
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