/i>[<i>n</i><sub>0</sub> -
<i>k</i><sub>0</sub>, <i>n</i><sub>1</sub> - <i>k</i><sub>1</sub>, ...,
<i>n</i><sub><i>d-1</i></sub> - <i>k</i><sub><i>d-1</i></sub>]<sup>*</sup>(where each dimension is periodic).  Because of this symmetry, we only
store the
<i>k</i><sub><i>d-1</i></sub> = 0...<i>n</i><sub><i>d-1</i></sub>/2+1elements of the <em>last</em> dimension (division by <em>2</em> is rounded
down).  (We could instead have cut any other dimension in half, but the
last dimension proved computationally conv