Sympy Summation with Indexed Variable
I Try to Create a Sympy Expression with a Sum with an Indexed Variable as Previous Explain Here However, I Can Not Do Lambdify of This Expression and Give an...
I try to create a sympy expression with a Sum with an indexed variable as previous explain here However, I can not do lambdify of this expression and give an array to get the sum calculated. Is this impossible?
2 Answers
Perhaps like this?
s = Sum(Indexed('x',i),(i,1,3))
f = lambda x: Subs(s.doit(), [s.function.subs(s.variables[0], j)
for j in range(s.limits[0][1], s.limits[0][2] + 1)], x).doit()
>>> f((30,10,2))
42
You can use lambdify. Just make sure the limits of the sum match the iterables of a numpy array.
from sympy import Sum, symbols, Indexed, lambdify
import numpy as np
x, i = symbols("x i")
s = Sum(Indexed('x',i),(i,0,3))
f = lambdify(x, s)
b = np.array([1, 2, 3, 4])
f(b)
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