CODEWITHSUNDEEP
pythontypeerrorsympy
user32882
user32882

Reputation: 5877

Integral inside sum gives index label error

Here's something I'm trying out based on this page: http://tutorial.math.lamar.edu/Classes/DE/FourierSineSeries.aspx

from sympy import *
f = Function('f')
B = IndexedBase('B')
x, L = symbols('x L', real=True)
n = Symbol('n', integer=True)
n = Idx(n, (0, oo))
Bn = Indexed('B', n)
m = Symbol('m', integer=True)
expr = sin(m*pi*x/L)
lhs = integrate(f(x)*expr, (x,-L,L))
rhs = Sum(Bn*integrate(expr*sin(n*pi*x/L), (x,-L,L)), n)

It crashes on the last line, stating that:

TypeError: Idx object requires an integer label.

The Idx object does, however, have an explicitly set integer label. Furthermore, an expression as Sum(Bn*sin(n*pi*x/L),n) works with no problems.

Is the fact that I am putting an integral inside the sum problematic? Or is it just a minor syntax problem?

Upvotes: 1

Views: 94

Answers (1)

S Raghav
S Raghav

Reputation: 1526

The issue is because the variable n is used both as a Symbol and a Idx object. The following code does not throw an error. (Though I am not sure if it serves your purpose)

from sympy import *
f = Function('f')
B = IndexedBase('B')
x, L = symbols('x L', real=True)
n = Symbol('n', integer=True)
n_index = Idx(n, (0, oo))
Bn = Indexed('B', n)
m = Symbol('m', integer=True)
expr = sin(m*pi*x/L)
lhs = integrate(f(x)*expr, (x,-L,L))
rhs = Sum(Bn*integrate(expr*sin(n*pi*x/L), (x,-L,L)), n_index)

Upvotes: 1

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