how to put output of a function in diagonal of matrix

how would i have a function output become the diagonal of a matrix, for instance

   function y=f(x)
   y= 3x+1;
   end

how do i put the output of this function as the diagonal of a matrix with 0s everywhere else. i've attempted some type of for loop but it doesnt seem to work

i.e. the diagonal should have y(0), y(1), y(2),... y(n),

for different values of n

Answer 1

[James Tursa]

If y is a vector, then simply

y = diag(y);

If y is a matrix and you are trying to pick off the diagonal, then e.g.,

y = diag(diag(y));

[akay]

y is the function, i would like the output of this function to be the diagonal of the matrix, whereas you're already assuming y has been allocated the values of the function

[Stephen23]

@akay: y is not a function, f if your function. The answer you have given puts y into the diagonal of a matrix. If this is not what you want please explain in more detail.

Answer 2

[Walter Roberson]

y = diag(3*x+1);