help with using matrix index from previous iteration.

hello guys, I hope you have a nice weekend. please, if anyone can help me with this problem related to the matrix index. Bellow is a part of my code.

d{11}=Q_{1:1}*(t(1))^3;
D{11}=(2/3)*d{11};
for ii=2:j
    k=ii;ss=ii-1;
    d{ii}=d{ss}+Q_{ii}*(((z(k))^3)-((z(k-1))^3));
    D{ii}=(2/3)*d{ii};
end

i am trying to use the previous matrix d{ss} to calculate the new one d{ii}. i need all ds to use them in another iteration. the problem is i have this error.

error using  + 
Matrix dimensions must agree.

Error in Untitled (line 46)
    d{ii}=d{ss}+Q_{ii}*(((z(k))^3)-((z(k-1))^3));

also i tried to use d{ii-1} and d{i-1i-1} but i always have the error message. please if there anyway how to insert the previous matrix in my iteration.

[Azzi Abdelmalek]

Format your question http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[Jonathan Epperl]

How about you look at the matrices in question, for instance using a break point? In particular, what is the dimension of d{10}? My assumption is it is an empty array, and that will get you that error.

[]+magic(2)
%Error using  + 
%Matrix dimensions must agree.