I do have a matrix A(n,n) and a matrix B(m,n) m<n and want to create a third matrix C(n,n) where C(i,j)= k if A(i,j)<=B(k,j) && if A(i,j)>B(k-1,j).

The question is to rank the element of each vector (column) in A(n,n) according to the order in B(m,n) and get a new matrix with these ranks. It is a classification of elements by column : example:

A = [0 4 7 ;
     1 3 5 ;
     3 3 6 ] 
B = [0 0 1 ; 
     3 1 2 ]

A(1,1)<=B(1,1)==>C(1,1)=1<---the index of zero in B;

A(2,1)>B(1,1)=0 && A(2,1)<=B(2,1) ==> C(2,1)=2

A(3,1)==B(2,1)> B(1,1)=0 ==> C(3,1)=2 and go next to the second column, then next one to get

   C=[1 2 2, C(:,2),C(:,3)]

[Image Analyst]

I don't understand the rule(s). Why does A(1,1) get compared to B(1,1) but the second element of the first column of A get compared to two elements of B, and the third element of the first column of A gets compared to B(2,1) but then B(2,1) gets compared to B(1,1)? Why do you need to do this complicated thing?

Answer 1

[Santhana Raj]

You can create three nested loops for i, j and k. and check for your condition:

if ((A(i,j)<=B(k,j) && (A(i,j)>B(k-1,j))

Take care that, when k=1, you cant check both the conditions and only the first conditions is to be applied.

Hope it helps.

[Youssef]

Thank you very much. I used a first condition to take care about the first row. I used the same code in 2015b version, and it gave me an error "Subscript indices must either be real positive integers or logicals.". But I run it in an old version (20114b) and it works!!!!