pythonsympysymbolic-integration

Integrate in sympy doesn't work for x*cos(n*pi*x/L), but DOES work for sqrt(1.)*x*cos(n*pi*x/L). Please see code snippets below

Code snippet 1:

from sympy import symbols, integrate, cos, pi
from numpy import sqrt
n = symbols('n', integer=True)
x, L = symbols('x L', real=True)
fs_coeff = integrate(sqrt(1.)*x*cos(n*pi*x/L), (x, 0, L))
print fs_coeff

And I get:

-1.0*Piecewise((0, n == 0), (0.101321183642338*L*2/n*2, True)) + 1.0*Piecewise((L**2/2, n == 0), (0.318309886183791*L**2*sin(3.14159265358979*n)/n + 0.101321183642338*L**2*cos(3.14159265358979*n)/n**2, True))

Code snippet 2:

from sympy import symbols, integrate, cos, pi
from numpy import sqrt
n = symbols('n', integer=True)
x, L = symbols('x L', real=True)
fs_coeff = integrate(x*cos(n*pi*x/L), (x, 0, L))
print fs_coeff

And I get an error:

Traceback (most recent call last):

File "test-sympy.py", line 6, in

fs_coeff = integrate(x*cos(n*pi*x/L), (x, 0, L))

...

ValueError: too many values to unpack

I'm using the latest Enthought Canopy python distribution, v. 1.3. Python version 2.7.6, SymPy 0.7.3.

If you have any insight on this, I'd appreciate it.

Solution

  • SymPy 0.7.3 is not the newest version. Try it in 0.7.4.1. This was a bug that has been fixed.

    >>> fs_coeff = integrate(x*cos(n*pi*x/L), (x, 0, L))
>>> fs_coeff
Piecewise((L**2/2, n == 0), ((-1)**n*L**2/(pi**2*n**2) - L**2/(pi**2*n**2), True))