Create correlation matrix

MathStatChem — Mon, 31 Mar 2025 14:09:25 GMT

I need to create a correlation matrix to use for some simulations. I want all the off-diagonal elements of the correlation to be the same value. Here is a simple script that does that, but I was wondering if there was a simpler way to do it.

names default to here(1);
// create correlation matrix with specified correlation
k=5;
r=0.9;
corr_matrix=J(k,k,r);
// diagonal elements equal to 1 by adding (1-r)
corr_matrix=corr_matrix + diag(J(k,1,1-r));

This creates the matrix

[1 0.9 0.9 0.9 0.9,
0.9 1 0.9 0.9 0.9,
0.9 0.9 1 0.9 0.9,
0.9 0.9 0.9 1 0.9,
0.9 0.9 0.9 0.9 1]

Re: Create correlation matrix

Jed_Campbell — Mon, 31 Mar 2025 14:33:45 GMT

I'm unaware of a simpler way, but in case you're wanting a simpler way because you're planning on using your code frequently, you could make it into a function, as per the example below. Then, calling it is simpler each time.

//function
make_cm = function ({k,r},
	corr_matrix=J(k,k,r);
	// diagonal elements equal to 1 by adding (1-r)
	corr_matrix=corr_matrix + diag(J(k,1,1-r)); 
);

//call the function
make_cm (5, .9);

topic Re: Create correlation matrix in Discussions

Create correlation matrix

Re: Create correlation matrix