I am having some troubles to get the logistic equation from its
differential form. For example:
sage: tau = var('tau') # proportionality constant
sage: k = var('k') # max population size
sage: t = var('t') # independent variable
sage: p = function('p', t) # dependent variable
sage: myode = tau*diff(p,t) == p*(1-p/k)
sage: sol(t) = desolve(de=myode, ivar=t, dvar=p)
sage returns:
-tau*log(-k + p(t)) + tau*log(p(t)) == c + t
Now, when I try to show the solution to the equation:
sage: plot(sol.subs(tau=20, k=10, c=1), 0, 100)
i've got the following error:
verbose 0 (4075: plot.py, generate_plot_points) WARNING: When plotting,
failed to evaluate function at 200 points.
verbose 0 (4075: plot.py, generate_plot_points) Last error message:
'unable to simplify to float approximation'
I would appreciate some help here.
Thanks in advance
Jose
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