Status: Accepted
Owner: ----
Labels: Type-Defect Priority-Medium CodeInCategory-Code
CodeInDifficulty-Medium
New issue 2830 by [email protected]: checkodesol needs to use force
http://code.google.com/p/sympy/issues/detail?id=2830
@@ -542,7 +542,11 @@ def test_1st_homogeneous_coeff_ode_check3():
# (False, x*(log(exp(-LambertW(C1*x))) +
LambertW(C1*x))*exp(-LambertW(C1*x) + 1))
eq3 = f(x) + (x*log(f(x)/x) - 2*x)*diff(f(x),x)
sol3 = Eq(f(x), x*exp(1 - LambertW(C1*x)))
- assert checkodesol(eq3, sol3, solve_for_func=False)[0]
+ assert checkodesol(eq3, sol3, solve_for_func=True)[0]
+ # and without an assumption about x and f(x), the implicit form
doesn't resolve, either:
+ # (False, (log(f(x)/x) + log(x/f(x)))*f(x))
So checkodesol() needs to be more aggressive, since dsolve() obtains these
logarithms by calling logcombine(force=True). An expand with force=True
should be used on expressions being tested or else (as shown above) terms
which should go to zero, don't:
log(f(x)/x) + log(x/f(x))
log(f(x)/x) + log(x/f(x))
_.expand(force=True)
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