How to assign values to a MATLAB matrix on the diagonal?

Question

Suppose I have an NxN matrix A, an index vector V consisting of a subset of the numbers 1:N, and a value K, and I want to do this:

 for i = V
     A(i,i) = K         


        

Answer 1

>> B=[0,4,4;4,0,4;4,4,0]

B =

     0     4     4
     4     0     4
     4     4     0

>> v=[1,2,3]

v =

     1     2     3

>> B(eye(size(B))==1)=v
%insert values from v to eye positions in B

B =

     1     4     4
     4     2     4
     4     4     3