MATLAB: How to read the data from vector

read data

a=randi(10000,[10000,1]);
b=randi(10000,[10000,1]);
c=randi(100,[10000,10000]);

My question is how to find the row index of c where the c equals 5 (a is the x coordinate and b is the y coordinate).

I can do it using loop:

index=zeros(length(a),1);
for i=1:length(a)
index(i)=(c(a(i),b(i))==5);
end
index1=find(index);

May I know how to do it more efficiently whithout the use of for loop?

You cannot. Your a values are up to 10000 but your c array is only 1000 on a side.

If you were to fix the ranges of a and b then

d = c(sub2ind(size(c), a, b));

There is no need to loop. Use logical indexing:

a=randi(5,10,1);
b=randi(5,10,1);
c=randi(5,10,1);
[a,b,c]
i = (a+b>c);
b(i) = c(i)-a(i);
[a,b,c]

 idx = sub2ind(size(C), A, B)
 result = max(C(idx));