可变大小的对称矩阵输出

Question

I am trying to create a function for the Mexican Hat wavelet, that allows for a variable output size (3x3, 5x5, 15x15, etc). The code below only works (gets a symmetrical shape) for a 5x5 input, but if it try to obtain a 15x15 output (d = 15), the result does not center the highest value in the middle.

a = np.empty([5, 5])

def mex(array):
    h = np.empty_like(array, dtype=np.float)
    print "Say the filter size (d)"
    d = int(raw_input("> "))
    for line in range(array.shape[0]):
        for col in range(array.shape[1]):
            x = col - (d - 1)/2
            y = (d - 1)/2 - line
            value = 0
            value = (1 - x**2 - y**2) * math.exp(-((x**2)+(y**2))/2)
            h[line, col] = value
    print h
    return h

b = mex(a)

This is the result for 5x5 input:

And this is the result for 15x15:

Thanks for any help! :)

Answer 1

You are only showing the bottom left corner of the hat. Because your mex function starts by creating a 5 x 5 matrix you then fill that with just that corner of the 15 x 15 thing you are trying to create. Which of course is not symmetrical.