--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sparse2cell.m	Thu Mar 03 14:00:27 2016 +0100
@@ -0,0 +1,28 @@
+% sparse2cell breaks a sparse matrix up into a cell matrix of sparse matrices.
+% any zero submatrix creates a empty cell in the cell matrix.
+%  A -- NxM sparse matrix
+%  d1, d2 -- vectors of sub matrix sizes for each dimensions. Must have sum(di) == Ni.
+% Example:
+%   C = sparse2cell(A,[5 10], [10 5])
+function C = sparse2cell(A, d1, d2)
+    [n, m] = size(A);
+    if n ~= sum(d1) || m ~= sum(d2)
+        error('sparse2cell:NonMatchingDim','The elements of d1 and d2 must sum to N and M.');
+    end
+
+    C = cell(length(d1), length(d2));
+    I = 1;
+    for i = 1:length(d1)
+        J = 1;
+        for j = 1:length(d2)
+            Asub = A(I:(I + d1(i)-1), J:(J + d2(j)-1));
+            if nnz(Asub) == 0
+                C{i,j} = [];
+            else
+                C{i,j} = Asub;
+            end
+            J = J + d2(j);
+        end
+        I = I + d1(i);
+    end
+end