On Sat, Nov 16, 2013 at 8:28 AM, David Pine <djp...@gmail.com> wrote: > The program at the bottom of this message returns the following runtime > warning: > > python test.py > test.py:5: RuntimeWarning: invalid value encountered in divide > return np.where(x==0., 1., np.sin(x)/x) > > The function works correctly returning > x = np.array([ 0., 1., 2., 3., 4., 5., 6., 7., 8., 9., > 10.]) > y = np.array([ 1. , 0.84147098, 0.45464871, 0.04704 , -0.18920062, > -0.19178485, -0.04656925, 0.09385523, 0.12366978, 0.04579094, > -0.05440211]) > > The runtime warning suggests that np.where evaluates np.sin(x)/x at all x, > including x=0, even though the np.where function returns the correct value of > 1. when x is 0. This seems odd to me. Why issue a runtime warning? Nothing > is wrong. Moreover, I don't recall numpy issuing such warnings in earlier > versions. > > import numpy as np > import matplotlib.pyplot as plt > > def sinc(x): > return np.where(x==0., 1., np.sin(x)/x) > > x = np.linspace(0., 10., 11) > y = sinc(x) > > plt.plot(x, y) > plt.show()
For what it's worth, you can see the different strategies that numpy and scipy use to work around this warning. https://github.com/numpy/numpy/blob/master/numpy/lib/function_base.py#L2662 https://github.com/scipy/scipy/blob/master/scipy/special/basic.py#L43 Numpy sinc uses a small number instead of zero. Scipy sinc disables the warning explicitly. _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
