Hi:
Sympy's dsolve solves
t = Symbol("t")
y = Function("y")
de = y(t).diff(t)+2*y(t) - t*exp(-2*t)
dsolve(de,y(t))
#y(t) == (C1 + t**2/2)*exp(-2*t)
and
t = Symbol("t")
y = Function("y")
de = y(t).diff(t)+2*y(t) - 2*cos(t)
dsolve(de,y(t))
#y(t) == (C1 + 2*exp(2*t)*sin(t)/5 + 4*exp(2*t)*cos(t)/5)*exp(-2*t)
instantly, but when I try the sum
t = Symbol("t")
y = Function("y")
de = y(t).diff(t)+2*y(t) - t*exp(-2*t) - 2*cos(t)
dsolve(de,y(t))
#y(t) == (C1 + t**2/2 + 2*exp(2*t)*sin(t)/5 + 4*exp(2*t)*cos(t)/5)*exp(-2*t)
Sympy takes 5 seconds (or more). I tested this both
with the debian sympy and with the latest spkg of Sympy in
Sage (the spkg version was much slower). I'm also on
a fairly old ubuntu machine.
Not a complaint really, just curious why this happens.
- David Joyner
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