Thanks as always for your useful SAS advice. Your column about the VECH and SQRVECH functions suggested a useful method for creating large correlation matrices (https://blogs.sas.com/content/iml/2012/03/21/creating-symmetric-matrices-two-useful-functions-with-strange-names.html). I enter each row of the upper triangular matrix, starting with the diagonal element, to make it easy to check data entry. As shown below, rows are not separated by commas. This approach can save a lot of typing, and typing mistakes, as the number of variables goes up.

R = sqrvech(
{1 .9
1}
);