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Animate plot of two piecewise functions

asked 2011-11-04 12:50:22 -0500

sagefan gravatar image

updated 2011-11-04 23:08:17 -0500

Consider a slightly modified version to the workaround to this question

sage: k = 5
sage: f = Piecewise([[(-2,1),k],[(1,4),x]])
sage: g =  Piecewise([[(-2,1),1],[(1,4),2*x]])
sage: P = plot(f,color='green')
sage: Q = plot(g,linestyle='--')
sage: P+Q

Is it possible to animate this plot say with k ranging from 0 to 10?

I tried:

k = 5
f = Piecewise([[(-2,1),k],[(1,4),x]])
g =  Piecewise([[(-2,1),1],[(1,4),2*x]])
P = plot(f,color='green')
Q = plot(g,linestyle='--')
X = P+Q
b = animate([X for k in srange(0,10)],xmin=0,xmax=4,figsize=[5,5])
b
b.show()

but it calculates for minutes and doesn't show up a result. (I tried examples from the documentation which worked fine).

I also tried this:

t = var('t')
k = var('k')

def f(t,k):
    if t <=1:
        return t
    else:
        return k


def g(t,k):
    if t <=1:
        return 1
    else:
        return 2*t

@interact
def _(k=(0,10)):
    p1=plot(f(t,k),(t,0,3),ymax=10,ymin=0,color='green')
    p2=plot(g(t,k),(t,0,3))
    show(p1 + p2)

However the piecewise defined functions don't work in this case.

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answered 2011-11-05 16:26:16 -0500

kcrisman gravatar image

Ok, this should work.

sage: f = lambda k: Piecewise([[(-2,1),k],[(1,4),x]])
sage: P = plot(f(5))
sage: show(P)
KeyboardInterrupt
sage: A = animate([plot(f(k)) for k in [0..10]]) 
sage: show(A)

Hopefully something similar would work in an interact...

If you've never seen them, then lambda functions are mysterious, but it turns out useful for exactly this kind of thing.

I think this is probably the only reasonable way to do it, since piecewise functions automatically treat any variable in them as the function inside.

sage: var('y,z')
(y, z)
sage: g = Piecewise([[(-2,1),y^2],[(1,4),-z^2]])
sage: plot(g)
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Ok, thanks. It works in both cases.

sagefan gravatar imagesagefan ( 2011-11-06 01:28:46 -0500 )edit
0

answered 2011-11-04 17:04:49 -0500

kcrisman gravatar image

updated 2011-11-05 16:18:30 -0500

Probably. Have you tried looking at

sage: animate?

and

sage: interact?

(the latter only works in the notebook). I would think one or both of these should work just fine.

Edit after update of question:

The first example will never work because of how Python handles variables.

sage: k = 5
sage: f = Piecewise([[(-2,1),k],[(1,4),x]])
sage: f
Piecewise defined function with 2 parts, [[(-2, 1), 5], [(1, 4), x]]

So k just slapped a 5 in there.

Let me try to see if I can come up with a workaround...

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Asked: 2011-11-04 12:50:22 -0500

Seen: 497 times

Last updated: Nov 05 '11