On Wed, Nov 28, 2012 at 9:18 AM, ThanhVu Nguyen <nguyenthanh...@gmail.com> wrote: > > I am wondering how to obtain the coefs and terms of a given expression in > sympy. For example, given the expression a**2+b+5*c+2, I want to get the > coefs [1,1,5,2] and the terms [a^2,b,c,1].
As a related question, recently I needed to extract the coefficient in a polynomial of t of a particular power of t: t**12*Ra(6)**2 + 2*t**11*Ra(5)*Ra(6) + 2*t**10*Ra(4)*Ra(6) + t**10*Ra(5)**2 + 2*t**9*Ra(3)*Ra(6) + 2*t**9*Ra(4)*Ra(5) + 2*t**8*Ra(2)*Ra(6) + 2*t**8*Ra(3)*Ra(5) + t**8*Ra(4)**2 + 2*t**7*Ra(1)*Ra(6) + 2*t**7*Ra(2)*Ra(5) + 2*t**7*Ra(3)*Ra(4) + 2*t**6*Ra(0)*Ra(6) + 2*t**6*Ra(1)*Ra(5) + 2*t**6*Ra(2)*Ra(4) + t**6*Ra(3)**2 + 2*t**5*Ra(0)*Ra(5) + 2*t**5*Ra(1)*Ra(4) + 2*t**5*Ra(2)*Ra(3) + 2*t**4*Ra(0)*Ra(4) + 2*t**4*Ra(1)*Ra(3) + t**4*Ra(2)**2 + 2*t**3*Ra(0)*Ra(3) + 2*t**3*Ra(1)*Ra(2) + 2*t**2*Ra(0)*Ra(2) + t**2*Ra(1)**2 + 2*t*Ra(0)*Ra(1) + Ra(0)**2 Given the above polynomial [which is just the expansion of (t**6*Ra(6) + t**5*Ra(5) + t**4*Ra(4) + t**3*Ra(3) + t**2*Ra(2) + t*Ra(1) + Ra(0))**2 given some function Ra()] I needed to query it for the coefficients of t**d for a particular d. From the answer by Aaron Meurer, it seems I can do: Poly(above_polynomial,t).allcoeffs()[-d-1] but it is not so elegant, and it also throws an IndexError if I query for some d greater than the degree of the polynomial whereas ideally a function something like: Poly.coeff_for_degree(d) would return 0 in such cases. Is such a function coeff_for_degree available? The input and output for such a function on the above (squared) polynomial would be what I got by doing: >>> for (p,v) in enumerate(reversed(Poly(mysum,t).all_coeffs())): print(p,v) 0 Ra(0)**2 1 2*Ra(0)*Ra(1) 2 2*Ra(0)*Ra(2) + Ra(1)**2 3 2*Ra(0)*Ra(3) + 2*Ra(1)*Ra(2) 4 2*Ra(0)*Ra(4) + 2*Ra(1)*Ra(3) + Ra(2)**2 5 2*Ra(0)*Ra(5) + 2*Ra(1)*Ra(4) + 2*Ra(2)*Ra(3) 6 2*Ra(0)*Ra(6) + 2*Ra(1)*Ra(5) + 2*Ra(2)*Ra(4) + Ra(3)**2 7 2*Ra(1)*Ra(6) + 2*Ra(2)*Ra(5) + 2*Ra(3)*Ra(4) 8 2*Ra(2)*Ra(6) + 2*Ra(3)*Ra(5) + Ra(4)**2 9 2*Ra(3)*Ra(6) + 2*Ra(4)*Ra(5) 10 2*Ra(4)*Ra(6) + Ra(5)**2 11 2*Ra(5)*Ra(6) 12 Ra(6)**2 Thanks! -- Shriramana Sharma -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com. To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
