desolve_rk4 cannot handle a piecewise function

asked 2014-02-20 18:26:00 +0100

updated 2014-02-20 18:31:21 +0100

I am trying to get a numeric solution to a differential equation involving a function that is piecewise (actually defined using an if/else statement). I successfully generated a slopefield using the lambda function, but desolve_rk4 seemingly cannot cope with this syntax. It seems to me that a numeric solver should be able to handle a function defined this way, but perhaps I am just doing something wrong?

Code:

var('t')
def f(t):
    if t<5:
        return 3
    else:
        return 0
V=function('V',t)
desolve_rk4(lambda t,V: ((f)-V)/(2.3*1.2),V, ics=(0,0),ivar=t)

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Short answer is that Maxima doesn't know what to do with such a Python lambda function, and this uses a Maxima functionality.

kcrisman ( 2014-02-20 20:31:21 +0100 )edit

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var('t s V') def f(t): if t<5: return 3 else: return 0 def rhs(V,s,t): return ((f(t)-V)/(2.3*1.2)) F=[SR(1),rhs] tlist=srange(0,10,0.1) ans=desolve_odeint(F,[0,10],tlist,[s,V],ivar=t) line(ans)

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