Status: Accepted
Owner: asmeurer
Labels: Type-Defect Priority-Medium Solvers EasyToFix WrongResult
New issue 2069 by asmeurer: classify_ode() doesn't catch homogeneous_coeff
when y is used
http://code.google.com/p/sympy/issues/detail?id=2069
In [37]: classify_ode(diff(v(r),r) + 2*k/r*v(r) - q0, v(r))
Out[37]:
(1st_linear, 1st_homogeneous_coeff_best,
1st_homogeneous_coeff_subs_indep_div_dep,
1st_homogeneous_coeff_subs_dep_div_indep, 1st_linear_Integral,
1st_homogeneous_coeff_subs_indep_div_dep_Integral, 1st
_homogeneous_coeff_subs_dep_div_indep_Integral)
In [38]: classify_ode(diff(v(r),r) + 2*k/r*v(r) + y, v(r))
Out[38]: (1st_linear, Bernoulli, 1st_linear_Integral, Bernoulli_Integral)
But these are the same, except for a trivial substitution on the constants
(y = -q0). I think the problem is that somewhere in classify_ode(), v(r)
is being replaced by Symbol('y'), instead of Symbol('y', dummy=True), so it
things the second one is actually diff(v(r), r) + 2*k/r*v(r) + v(r).
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