Return vector of coefficients of a symbolic polynomial.
In the two-input form, the second argument x specifies the free variable; in this case this function returns a row vector c of symbolic expressions. The coefficients correspond to decreasing exponent of the free variable. Example:
syms x y sym2poly(2*x^2 + 3*x - pi, x) ⇒ (sym) [2 3 -π] (1×3 matrix) sym2poly(x^2 + y*x, x) ⇒ (sym) [1 y 0] (1×3 matrix)
Warning: Using the single-argument form, the coefficient vector
c is a plain numeric vector (double). This is for compatibility
with the Matlab Symbolic Math Toolbox.
We suggest making this clear in your code by explicitly casting to double,
as in:
syms x double(sym2poly(pi*x^3 + 3*x/2 + exp(sym(1)))) ⇒ 3.1416 0 1.5000 2.7183
You may prefer specifying X or using coeffs:
coeffs(pi*x^3 + 3*x/2 + exp(sym(1)), 'all') ⇒ (sym) [π 0 3/2 ℯ] (1×4 matrix)
If p is not a polynomial the result has no warranty. SymPy can certainly deal with more general concepts of polynomial but we do not yet expose all of that here.
See also: poly2sym, @sym/coeffs, polyval, roots.
Package: symbolic