Do you really need this (implemented with loops):
[d1,d2,d3] = size(gridblock);
sum_oipsc = 0;
for i = 1:d1
for j = 1:d2
for k = 1:d3
sum_oipsc = sum_oipsc + gridblock(i,j,k).oipsc;
end
end
end
If that is the case, then the solution would be as simple as:
sum_oipsc2 = sum([gridblock(:).oipsc])
