sinc bug

[j3pa...@gmail.com]

Hi,

I think there is an error when `lambdifying` the sinc function, at least using 'numpy'. Sympy defines the sinc function as unnormalized; i.e sin(x)/x, while numpy defines it as normalized sin(pi.x)/(pi.x). So, the evaluation for [-1, 0, 1] is not the same:

>>> import sympy as sp

>>> f = sp.lambdify(x, sp.sinc(x), "numpy")

>>> f([-1, 0, 1])

array([  3.89817183e-17,   1.00000000e+00,   3.89817183e-17])

BUT

>>> s = sp.sinc(x)

>>> s.subs(x, -1).evalf()

0.841470984807897

>>> s.subs(x, 1).evalf()

0.841470984807897

I'm used to signal processing so I would prefer the normalized definition. In any case, the functions must be 'aligned'.

Regards,

José Parera