On Mon, Dec 14, 2020 at 04:47:44PM -0800, 'Nasser M. Abbasi' via FriCAS -
computer algebra system wrote:
> I am learning the syntax of using Fricas to solve an ode. I am using 8.10
> chapter in this link for reference
>
> http://fricas.github.io/book.pdf
>
> I think I am entering it correctly, but it gives me an error. Fricas 1.3.6
>
> y:=operator 'y
> ode := x^3* D(y x, x)^2+x*D(y x, x)- y x=0
> solve(ode, y, x)
>
>
> >> Error detected within library code:
> getlincoeff: not an appropriate ordinary differential equation
>
> Does this mean Fricas can not solve nonlinear ode's and Am I making a
> syntax error somewhere?
FriCAS can solve linear equations of "arbitrary" order (expect
troubles around order 4 or 5). It can solve nonlinear
equations of first order, but derivative must in linear
form. AFAICS your example can be rewriten as
ode := D(y x, x) = sqrt(y(x)/x^3 - D(y(x), x)/x^2)
solve(ode, y, x)
which gives "failed" because FriCAS does not know how
to solve this equation (but some other work after
solving for derivative).
Arguably, Fricas should automaticaly solve for derivative
(and some types of equations can be solved without
explicitely solving for derivative), but currently
this is not done.
--
Waldek Hebisch
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