I'm using symbolic math in Julia. When I do the differentiation it comes out very nicely, but I cant get the coefficients out
using SymPy
@vars x y
z = x*(10 + 5*x + 4*y)
dz = diff(z,x)
x_s = solveset(dz,x)
how do I get the the coefficients out of x_s?
You can use elements to get the elements of a finite sets as an array:
julia> elements(s)
1-element Array{Sym,1}:
-2*y/5 - 1
To get the coefficients can be done different ways, but here we convert the value to a Polynomial type, then use its coeffs method:
julia> p = sympy.Poly(elements(s)[1], y)
Poly(-2/5*y - 1, y, domain='QQ')
julia> p.coeffs()
2-element Array{Sym,1}:
-2/5
-1
As per my comment, the following works but isn't exactly what I'd describe as pretty:
julia> x_s.__pyobject__.args[1].__pyobject__.args[1]
-1
julia> x_s.__pyobject__.args[1].__pyobject__.args[2]
-2⋅y
─────
5
julia> x_s.__pyobject__.args[1].__pyobject__.args[2].__pyobject__.args[1]
-2/5
I couldn't find an accessor function in Sympy.jl that simplifies this, but as you say this could be the basis for rolling your own.