Hi, I'd like to numerically integrate a simple pendulum problem:
y'' = -9.8*cos(y)
y(0) = 0
y'(0) = 0
I have tried this code (based on the Lotka-Volterra example in the Sage
documentation):
from sage.calculus.desolvers import desolve_odeint
y,yd = var('y,yd')
f = [0,-9.8*cos(y)]
v = [y,yd]
t = srange(0,10,0.1)
ci = [0,1]
sol = desolve_odeint(f,ci,t,v,rtol=1e-3,atol=1e-4,h0=0.1,hmax=1,hmin=1e-4,
mxstep=1000)
p2 = line(zip(t,sol[:,0]))
p2.show()
which gave this output:
Traceback (most recent call last): sol = desolve_odeint(f,ci,t,v,rtol=
1e-3,atol=1e-4,h0=0.1,hmax=1,hmin=1e-4,mxstep=1000)
File "", line 1, in <module>
File "/tmp/tmpowXVlu/___code___.py", line 9, in <module>
sol = desolve_odeint(f,ci,t,v,rtol=_sage_const_1en3 ,atol=_sage_const_1en4
,h0=_sage_const_0p1 ,hmax=_sage_const_1 ,hmin=_sage_const_1en4
,mxstep=_sage_const_1000
)
File
"/home/sage/sage-6.6/local/lib/python2.7/site-packages/sage/calculus/desolvers.py"
, line 1487, in desolve_odeint
all_vars.update(set(de.variables()))
File "sage/structure/element.pyx", line 430, in sage.structure.element.
Element.__getattr__ (build/cythonized/sage/structure/element.c:4625)
File "sage/structure/misc.pyx", line 257, in
sage.structure.misc.getattr_from_other_class
(build/cythonized/sage/structure/misc.c:1772)
AttributeError: 'sage.rings.integer.Integer' object has no attribute
'variables'
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