Defining formulas for diagonal and offdiagonal elements of a matrix

I have a vector M. I want to create a matrix s.t.

A(j,j) = M(j)*(1 + (M(j)-1)*roh_w)

A(j,k) = M(j)*M(k)*roh_b, whenever j!=k.

I can do

A = diag(M.*(1+(M-1)*roh_w) - M.^2*roh_b);

A = A + M.'*M*roh_b;

i.e., I first create a diagonal matrix s.t.

A(j,j) = M(j)*(1 + (M(j)-1)*roh_w) - M(j)*M(k)*roh_b,

I then add a matrix whose effect is canceled out by the second term right above for diagonal elements. Is there a prettier way of doing this?

Quintessentially, is there a one-liner code s.t. you give formula for diagonal elements and nondiagonal elements, e.g., A = FUNCTION(formula for diagonal elements, formula for nondiagonal elements)?

I'd appreciate any and all help. Thank you

Best, John

Answer 1

[Roger Stafford]

   A = eye(length(M))*f1+(1-eye(length(M))*f2;

where f1 is the formula for the diagonal elements and f2 that for the off-diagonal elements.

[Roger Stafford]

The following is preferable. Let M be a row vector of size 1-by-m.

   A = diag(M.*(1+(M-1)*roh_w))+(1-eye(m)).*(M.'*(M*roh_b));

[Jeong Ho]

Dear Roger,

Thank you so much for your help. It works like a charm! Thank you!

Best,

John