I thought I already sent in a patch to fix this. Aaron Meurer
Sent from my iPod Touch. On May 14, 2009, at 9:53 AM, Priit Laes <plaes...@gmail.com> wrote: > Bernoulli ODE has one case where it should be solved using different > algorithm. Currently we don't detect it and hilarity ensues in the > form > of divide by zero :) > > https://code.plaes.org/git/sympy.git/commit/?h=patches-0514&id=56524bf458074ac9635f537ef6f83c4727ea7a56 > > > > > > From ffc4f78386316e5a876d7d83672b72319fa01140 Mon Sep 17 00:00:00 > 2001 From: Priit Laes Date: Sat, 11 Apr 2009 21:15:13 +0300 Subject: > [PATCH 2/2] Added corner case for Bernoulli equation. Signed-off-by: > Priit Laes --- sympy/solvers/solvers.py | 8 ++++++-- sympy/solvers/ > tests/test_solvers.py | 1 + 2 files changed, 7 insertions(+), 2 > deletions(-) diff --git a/sympy/solvers/solvers.py b/sympy/solvers/ > solvers.py index 16a14c2..e6928dc 100644 --- a/sympy/solvers/ > solvers.py +++ b/sympy/solvers/solvers.py @@ -569,6 +569,7 @@ def > solve_ODE_first_order(eq, f): and Bernoulli cases are implemented. > """ from sympy.integrals.integrals import integrate + C1 = > Symbol("C1") x = f.args[0] f = f.func @@ -581,16 +582,19 @@ def > solve_ODE_first_order(eq, f): if r: t = exp(integrate(r[b]/r[a], x)) > tt = integrate(t*(-r[c]/r[a]), x) - return (tt + Symbol("C1"))/t + > return (tt + C1)/t #Bernoulli case: a(x)*f'(x)+b(x)*f(x)+c(x)*f(x)^n > = 0 n = Wild('n', exclude=[f(x)]) r = eq.match(a*diff(f(x),x) + > b*f(x) + c*f(x)**n) if r: + if r[n] == 1: + return C1*exp(integrate(- > (r[b]+r[c]), x)) + # r[n] != 1 ie, the real bernoulli case t = > exp((1-r[n])*integrate(r[b]/r[a],x)) tt = (r[n]-1)*integrate(t*r[c]/ > r[a],x) - return ((tt + Symbol("C1"))/t)**(1/(1-r[n])) + return ((tt > + C1)/t)**(1/(1-r[n])) #other cases of first order odes will be > implemented here diff --git a/sympy/solvers/tests/test_solvers.py b/ > sympy/solvers/tests/test_solvers.py index 8d02fb7..a4d9d1f 100644 > --- a/sympy/solvers/tests/test_solvers.py +++ b/sympy/solvers/tests/ > test_solvers.py @@ -158,6 +158,7 @@ def test_ODE_first_order(): > assert dsolve(3*f(x).diff(x) -1, f(x)) == x/3 + C1 assert > dsolve(x*f(x).diff(x) -1, f(x)) == log(x) + C1 assert > dsolve(x*f(x).diff(x)+f(x)-f(x)**2,f(x)) == 1/(x*(C1 + 1/x)) + > assert dsolve(f(x).diff(x)+x*f(x)-f(x),f(x)) == C1*exp(x - x**2/2) > def test_ODE_second_order(): f = Function('f') -- 1.6.3 --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sympy-patches" group. To post to this group, send email to sympy-patches@googlegroups.com To unsubscribe from this group, send email to sympy-patches+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sympy-patches?hl=en -~----------~----~----~----~------~----~------~--~---
