The code is able to solve for "x**2*Derivative(f(x), x, x) -
2*x*Derivative(f(x), x) + 2*f(x) - log(x) = 0" but is giving very complex
solution. Is there any way to simplify complex equations.
The solution it is giving is
"(C1*sin(log(x)*Abs(im(sqrt(-log(x)**2)/log(x)**2) - arg(x)/(log(Abs(x))**2
+ arg(x)**2))) + C2*cos((im(sqrt(-log(x)**2)/log(x)**2) -
arg(x)/(log(Abs(x))**2 +
arg(x)**2))*log(x)))*exp((re(sqrt(-log(x)**2)/log(x)**2) +
log(Abs(x))/(log(Abs(x))**2 + arg(x)**2))*log(x)) +
(C3*sin(log(x)*Abs(im(sqrt(-log(x)**2)/log(x)**2) + arg(x)/(log(Abs(x))**2
+ arg(x)**2))) + C4*cos(-(-im(sqrt(-log(x)**2)/log(x)**2) -
arg(x)/(log(Abs(x))**2 +
arg(x)**2))*log(x)))*exp((-re(sqrt(-log(x)**2)/log(x)**2) +
log(Abs(x))/(log(Abs(x))**2 + arg(x)**2))*log(x)) + log(x)/2 + 3/4"
while the actual solution is "c1*x + c2*x**2 + log(x)/2 + 3/4"
Here last two term that is particular solution is coming same, there is
problem with general solution.
But code is not able to solve if I replace log(x) with any thing else like
"x or x**2" in the question, in this case it is giving this error
```File "sympy/solvers/ode.py", line 3963, in
_solve_undetermined_coefficients
"(unable to solve for coefficients)." % eq)
NotImplementedError: Could not solve `2*f(x) - exp(x) - 3*Derivative(f(x),
x) + Derivative(f(x), x, x)` using the method of undetermined coefficients
(unable to solve for coefficients)```
@Ondrej @Aaron Any comments on this?
On Friday, March 21, 2014 5:42:41 AM UTC+5:30, Aaron Meurer wrote:
>
> The error message gives a hint (unable to solve for coefficients). So
> somehow the point where solve() is called on the coefficients it
> doesn't work. You'll have to put some print statements in the code to
> see what is the input and output of solve that doesn't work.
>
> Aaron Meurer
>
> On Thu, Mar 20, 2014 at 1:50 PM, Kundan Kumar
> <[email protected] <javascript:>> wrote:
> > Aaron,
> > When I am running dsolve for nonhomogeneous euler equation it is giving
> > error
> >
> > NotImplementedError: Could not solve `-x + 2*f(x) - exp(x) -
> > 3*Derivative(f(x), x) + Derivative(f(x), x, x)` using the method of
> > undetermined coefficients (unable to solve for coefficients File
> > "sympy/solvers/ode.py", line 561, in dsolve
> > return _helper_simplify(eq, hint, hints, simplify)
> > File "sympy/solvers/ode.py", line 583, in _helper_simplify
> > rv = odesimp(solvefunc(eq, func, order, match), func, order, hint)
> > File "sympy/solvers/ode.py", line 3300, in
> > ode_nth_linear_euler_eq_nonhomogeneous
> > return ode_nth_linear_constant_coeff_undetermined_coefficients(eq,
> func,
> > order, match).replace(x,log(x))
> > File "sympy/solvers/ode.py", line 3862, in
> > ode_nth_linear_constant_coeff_undetermined_coefficients
> > return _solve_undetermined_coefficients(eq, func, order, match)
> > File "sympy/solvers/ode.py", line 3963, in
> > _solve_undetermined_coefficients
> > "(unable to solve for coefficients)." % eq)
> > NotImplementedError: Could not solve `-x + 2*f(x) - exp(x) -
> > 3*Derivative(f(x), x) + Derivative(f(x), x, x)` using the method of
> > undetermined coefficients (unable to solve for coefficients))
> >
> > I read the code of undetermined coefficients, this error comes only when
> > there is no value of "list" of coefficients of Particular solution like
> a0,
> > a1, ..
> > Since the equation it is showing is perfect and it can easily solved by
> > method of undetermined coefficients. I checked collectterms, r['list'],
> > r['sol'], these are working fine. The most probably error may be arising
> due
> > to trialset.
> > Since you know the inside-out of this undetermined function, can you
> suggest
> > why this is happening?
>
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