#10246: Can't get symbol from callable function x |--> x
-----------------------------------+----------------------------------------
Reporter: kcrisman | Owner: burcin
Type: defect | Status: needs_review
Priority: critical | Milestone: sage-4.7
Component: symbolics | Keywords: plot, beginner
Author: Karl-Dieter Crisman | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
-----------------------------------+----------------------------------------
Changes (by newvalueoldvalue):
* status: new => needs_review
* author: => Karl-Dieter Crisman
Old description:
> From [http://ask.sagemath.org/question/198/plotting-x-free-variable-error
> this] ask.sagemath question:
>
> {{{
> I was plotting sin(x)/x and also wanted a seperate plot of sin(x) and x
> so I could visualize those components as well. However I get an error
> when plotting x saying "free variable x -> x". If I add a coefficient to
> h(x) such as h(x) = 1.0001*x then it works fine.
>
> This is the code I am using:
>
> f(x) = sin(x)/x
> g(x) = sin(x)
> h(x) = x
>
> fig1 = plot(f,-10,10,rgbcolor='green')
> fig2 = plot(g,-10,10,rgbcolor='purple')
> fig3 = plot(h,-10,10,rgbcolor='red')
>
> figure = fig1 + fig2 + fig3
> show(figure,xmin=-10,xmax=10,ymin=-10,ymax=10,figsize=[8,8],fontsize=20)
> }}}
>
> The underlying problem is
> {{{
> The exception arises in
> `sage.symbolic.expression_conversions.FastFloatConverter.symbol`:
>
> try:
> return self.ff.fast_float_constant(float(ex))
> except TypeError:
> raise ValueError, "free variable: %s" % repr(ex)
>
> so that it assumes if a callable expression doesn't have the variable, it
> must be a constant. However, it before this asks for `if name in vars`
> and `if name in svars`, but here the `name` is `'x |--> x'`.
>
> So what we need to do is fix it so that if the operator is `None` in the
> previous traceback in your error message, we check for this case
> explicitly, where the name isn't just one of the variables.
> }}}
New description:
From [http://ask.sagemath.org/question/198/plotting-x-free-variable-error
this] ask.sagemath question:
{{{
I was plotting sin(x)/x and also wanted a seperate plot of sin(x) and x so
I could visualize those components as well. However I get an error when
plotting x saying "free variable x -> x". If I add a coefficient to h(x)
such as h(x) = 1.0001*x then it works fine.
This is the code I am using:
f(x) = sin(x)/x
g(x) = sin(x)
h(x) = x
fig1 = plot(f,-10,10,rgbcolor='green')
fig2 = plot(g,-10,10,rgbcolor='purple')
fig3 = plot(h,-10,10,rgbcolor='red')
figure = fig1 + fig2 + fig3
show(figure,xmin=-10,xmax=10,ymin=-10,ymax=10,figsize=[8,8],fontsize=20)
}}}
The underlying problem is
{{{
The exception arises in
`sage.symbolic.expression_conversions.FastFloatConverter.symbol`:
try:
return self.ff.fast_float_constant(float(ex))
except TypeError:
raise ValueError, "free variable: %s" % repr(ex)
so that it assumes if a callable expression doesn't have the variable, it
must be a constant. However, it before this asks for `if name in vars`
and `if name in svars`, but here the `name` is `'x |--> x'`.
So what we need to do is fix it so that if the operator is `None` in the
previous traceback in your error message, we check for this case
explicitly, where the name isn't just one of the variables.
}}}
----
Apply attachment:trac_10246-callable-x.patch
--
Comment:
Ready for review. This should fix the problem, and I tried to do it in a
relatively elegant way. Unfortunately, there really is no such elegant
way, since `symbol` shouldn't be relying on strings anyway, right? Oh
well.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10246#comment:3>
Sage <http://www.sagemath.org>
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