Puzzle 11: conv_spec does not implement convolution

[BrandonConder]

The conv_spec function does not implement convolution:

def conv_spec(a, b):
    out = np.zeros(*a.shape)
    len = b.shape[0]
    for i in range(a.shape[0]):
        out[i] = sum([a[i + j] * b[j] for j in range(len) if i + j < a.shape[0]])
    return out

One of the inputs should be index-reversed (see wikipedia)

We can also confirm the error using numpy.convolve

np.convolve(a, b, mode='same')

Test 1 output:

array([ 0,  1,  4,  7, 10, 13])

which conflicts with the conv_spec output:

Spec : [ 5.  8. 11. 14.  5.  0.]

Test 2 output:

array([ 0,  1,  4, 10, 16, 22, 28, 34, 40, 46, 52, 58, 64, 70, 76])

which also conflicts with the conv_spec output:

Spec : [14. 20. 26. 32. 38. 44. 50. 56. 62. 68. 74. 80. 41. 14.  0.]

[srush]

meh, it's roughly a convolution up to some corner case details.