Define x as symbolic variable in many animate examples

[umedoblock]

The animated plots examples in the documentation at

• https://doc.sagemath.org/html/en/reference/plotting/sage/plot/animate.html

include an example where x = lambda t: cos(t)
and y = ... are used for a parametric plot.

Many subsequent examples fail with a type error
if run without resetting x to its default value,
either with reset('x') or with x = SR.var('x').

sage: a = animate([plot(x^2 + n) for n in range(4)], ymin=0, ymax=4)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-...-...> in <module>
----> 1 a = animate([plot(x**Integer(2) + n) for n in ...], ymin=..., ymax=...)

<ipython-input-...-...> in <listcomp>(.0)
----> 1 a = animate([plot(x**Integer(2) + n) for n in ...], ymin=..., ymax=...)

.../site-packages/sage/rings/integer.pyx in sage.rings.integer.Integer.__pow__ (build/cythonized/sage/rings/integer.c:14496)()
   2153             return coercion_model.bin_op(left, right, operator.pow)
   2154         # left is a non-Element: do the powering with a Python int
-> 2155         return left ** int(right)
   2156
   2157     cpdef _pow_(self, other):

TypeError: unsupported operand type(s) for ** or pow(): 'function' and 'int'

sage: a = animate([sin(x + float(k)) for k in srange(0,2*pi,0.7)],
....:             xmin=0, xmax=2*pi, ymin=-1, ymax=1, figsize=[2,1])
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-...> in <module>
----> 1 a = animate([sin(x + float(k)) for ...],
      2             xmin=..., xmax=..., ymin=..., ymax=..., figsize=...)

<ipython-input-...> in <listcomp>(.0)
----> 1 a = animate([sin(x + float(k)) for ...],
      2             xmin=..., xmax=..., ymin=..., ymax=..., figsize=...)

TypeError: unsupported operand type(s) for +: 'function' and 'float'

sage: a = animate([sin(x + float(k)) for k in srange(0,2*pi,0.7)],
....:                xmin=0, xmax=2*pi, figsize=[2,1])
....:
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-...> in <module>
----> 1 a = animate([sin(x + float(k)) for ...],
      2                xmin=..., xmax=..., figsize=...)

<ipython-input-...> in <listcomp>(.0)
----> 1 a = animate([sin(x + float(k)) for ...],
      2                xmin=..., xmax=..., figsize=...)

TypeError: unsupported operand type(s) for +: 'function' and 'float'

CC: @slel @mkoeppe

Component: graphics

Keywords: SR.var('x')

Author: Michael Orlitzky

Branch/Commit: e73cd12

Reviewer: Samuel Lelièvre

Issue created by migration from https://trac.sagemath.org/ticket/33264

[slel]

comment:1

Did you redefine x before that?

Try running reset('x') and running the examples again.

[slel]

comment:2

All the examples work fine for me in a fresh Sage session

• using the Sage-macOS 9.5 prerelease
• or using Sage 9.5 final, built from source

If I first redefine x as a function, e.g.

sage: x = lambda t: t + 1

then the failures in the ticket description arise.

Resetting x to its starting value with

sage: reset('x')

solves the issues, and the examples work fine again.

[slel]

comment:3

This seems like user error rather than a defect in Sage.

Propose to close as invalid.

[umedoblock]

comment:4

Hello slelievre.

You said "redefine x" means below sentence ?

x = lambda t: cos(t)

If it's correct, I redefined.

I tried running reset('x') and running the examples again.

Then TypeError disappeared.

Thanks slelievre.

I'm a beginner of sagemath, so I have no idea how to recovery from TypeError.

And I couldn't run below sentence.

reset('x')

I believe that all of the sagemath beginner cannot recovery from TypeError.

Please change document of "make_image(frame, filename, **kwds)" in Animated plots.

EXAMPLES:

from sage.plot.animate import Animation
class MyAnimation(Animation):
   def make_image(self, frame, filename, **kwds):
       P = parametric_plot(frame[0], frame[1], **frame[2])
       P.save_image(filename,**kwds)

t = var('t')

vvvvvvvvvvvvvvvvvvvv
x = lambda t: cos(t)
^^^^^^^^^^^^^^^^^^^^

y = lambda n,t: sin(t)/n
B = MyAnimation([([x(t), y(i+1,t)],(t,0,1), {'color':Color((1,0,i/4)), 'aspect_ratio':1, 'ymax':1}) for i in range(4)])

d = B.png(); v = os.listdir(d); v.sort(); v  # long time
['00000000.png', '00000001.png', '00000002.png', '00000003.png']
B.show()  # not tested

class MyAnimation(Animation):
   def make_image(self, frame, filename, **kwds):
       G = frame.plot()

G.set_axes_range(floor(G.xmin()),ceil(G.xmax()),floor(G.ymin()),ceil(G.ymax()))
       G.save_image(filename, **kwds)

B = MyAnimation([graphs.CompleteGraph(n) for n in range(7,11)], figsize=5)
d = B.png()
v = os.listdir(d); v.sort(); v
['00000000.png', '00000001.png', '00000002.png', '00000003.png']
B.show()  # not tested

[orlitzky]

comment:5

In gh-umedoblock's defense, our examples do rely on some implicit magic, the symbolic variable x being automatically defined whenever sage starts or the doctest environment resets. I would much rather see us begin them all with x = SR.var("x") so that they're truly copy/paste-able, but I expect I'd be pelted with tomatoes if I proposed it.

[slel]

comment:6

Replying to @orlitzky:

In gh-umedoblock's defense, our examples do rely on some implicit magic, the symbolic variable x being automatically defined whenever sage starts or the doctest environment resets. I would much rather see us begin them all with x = SR.var("x") so that they're truly copy/paste-able [...]

Huge +1 from me.

[orlitzky]

comment:7

It looks like maybe there's a reason to propose this that won't make me look like a busybody: #32721

[umedoblock]

comment:8

Do you irritate me ?

Sorry.

I insert reset('x') under MyAnimation()

And animate() doesn't raise TypeError.

So please insert reset('x') under MyAnimation().

from sage.plot.animate import Animation
class MyAnimation(Animation):
    def make_image(self, frame, filename, **kwds):
        P = parametric_plot(frame[0], frame[1], **frame[2])
        P.save_image(filename,**kwds)

t = var('t')
x = lambda t: cos(t)
y = lambda n,t: sin(t)/n
B = MyAnimation([([x(t), y(i+1,t)],(t,0,1), {'color':Color((1,0,i/4)), 'aspect_ratio':1, 'ymax':1}) for i in range(4)])

vvvvvvvvvv
reset('x')
^^^^^^^^^^

d = B.png(); v = os.listdir(d); v.sort(); v  # long time
B.show()  # not tested

a = animate([plot(x^2 + n) for n in range(4)], ymin=0, ymax=4)
d = a.png(); v = os.listdir(d); v.sort(); v  # long time

[slel]

comment:9

Instead of reset('x'), you can also use x = SR.var('x').

I agree many documentation examples would be improved
if they started with that.

[umedoblock]

comment:10

Improved.

And works it.

Thanks slelieve and mjo.

from sage.plot.animate import Animation
class MyAnimation(Animation):
    def make_image(self, frame, filename, **kwds):
        P = parametric_plot(frame[0], frame[1], **frame[2])
        P.save_image(filename,**kwds)

t = var('t')
x = lambda t: cos(t)
y = lambda n,t: sin(t)/n
B = MyAnimation([([x(t), y(i+1,t)],(t,0,1), {'color':Color((1,0,i/4)), 'aspect_ratio':1, 'ymax':1}) for i in range(4)])

vvvvvvvvvvvvvvv
x = SR.var('x')
^^^^^^^^^^^^^^^

d = B.png(); v = os.listdir(d); v.sort(); v  # long time
B.show()  # not tested

a = animate([plot(x^2 + n) for n in range(4)], ymin=0, ymax=4)
d = a.png(); v = os.listdir(d); v.sort(); v  # long time

[orlitzky]

Commit: e73cd12

[orlitzky]

comment:11

One down, a million to go.

---

New commits:

e73cd12

Trac #33264: add "x = SR.var('x')" to several animation examples.

[orlitzky]

Branch: u/mjo/ticket/33264

[orlitzky]

Author: Michael Orlitzky

[slel]

comment:13

That will help!

[slel]

Reviewer: Samuel Lelièvre

[slel]

Changed keywords from none to SR.var('x')

[vbraun]

Changed branch from u/mjo/ticket/33264 to e73cd12