MATLAB Programming

Comma-Separated Lists
numDims = ndims(x);
idx = cell(1, numDims);
for k = 1:numDims
m = size(x, k);
p = ceil(m/2);
idx{k} = [p+1:m 1:p];
end
y = x(idx{:});
The function stores the index vectors in cell array idx. Building this cell array
is relatively simple. For each of the N dimensions, determine the size of that
dimension and find the integer index nearest the midpoint. Then, construct a
vector that swaps the two halves of that dimension.
By using a cell array to store the index vectors and a comma-separated list
for the indexing operation, fftshift shifts arrays of any dimension using
just a single operation: y = x(idx{:}). If you were to use explicit indexing,
you would need to write one if statement for each dimension you want the
function to handle:
if ndims(x) == 1
y = x(index1);
else if ndims(x) == 2
y = x(index1, index2);
end
Another way to handle this without a comma-separated list would be to loop
over each dimension, converting one dimension at a time and moving data
each time. With a comma-separated list, you move the data just once. A
comma-separated list makes it very easy to generalize the swapping operation
to an arbitrary number of dimensions.
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