function convolve (a, b) {
  return NdArray.new(a).convolve(b);
}
Convolve 2 N-dimensionnal arrays

@note: Arrays must have the same dimensions and a must be greater than b.
@note: The convolution product is only given for points where the signals overlap completely. Values outside the signal boundary have no effect. This behaviour is known as the 'valid' mode.

@param {Array|NdArray} a
@param {Array|NdArray} b