How to update a matrix with the node number

Hello

I have a circular geometry which is discretised by triangular elements. Now suppose the total number of triangle is 4 with 3 nodes like T=[1 2 3;6 5 8;8 11 4;10 3 12] and boundary nodes are B=[1 3 5 10 12]. Now boundary condition for each boundary node of a triangle Q=7.5 and size of Q is 3x3.

Q=zeros(3,3);
for i=1:size(T,1)
    n=T(i,:) %nodes of each triangle
    z=intersect(n,B); %boundary node present in each triangle
    if(z==n(1,1))
        Q(1,1)=7.5;
        if(z==n(1,2))
            Q(2,1)=7.5;
            if(z==n(1,3))
                Q(3,1)=7.5;
            end
        end
    end
end

This code is not working. I didn't get the matrix like for 1st triangle Q=[7.5 0 0;0 0 0;7.5 0 0], for 2nd triangle Q=[0 0 0;7.5 0 0;0 0 0], for 3rd triangle Q=[0 0 0;0 0 0;0 0 0], for 4th triangle Q=[7.5 0 0;7.5 0 0;7.5 0 0]

Please help me.