How to assign values in an identity matrix?

Simple question, but say I have a 3x3 identity matrix:

 I = eye(3)

 I =

     1     0     0
     0     1     0
     0     0     1

And I want to change the upper right two elements to, say, 2 and 4:

 I =

     1     0     2
     0     1     4
     0     0     1

Is there a function that will allow me to do this?

Answer 1

[James Tursa]

For this specific question, simple indexed assignment:

I(1:2,end) = [2;4];

But what is your actual problem?