you have to design the dimension of your output matrix, example if it is 10x3 set i(number of rows) and j(number of columns), than for loop will begin like loop#1 i=1 j=1 loop#2 i=1 j=2 loop#3 i=1 j=3 then loop#4 i=2 j=1 loop#5 i=2 j=2 loop#6 i=2 j=3 ...etc
for i=1:10
for j=1:3
x=randn(1);
a(i,j)=x ;
end
end
you can always use debugging mode https://www.mathworks.com/help/matlab/matlab_prog/debugging-process-and-features.html to understand how matlab treat your loop
