The name of a matrix must be a valid SAS name: a character string that contains between 1 and 32 characters, begins with a letter or underscore, and contains only letters, numbers, and underscores. You associate a name with a matrix when you create or define the matrix. A matrix name exists independently of values. This means that you can change the values associated with a particular matrix name, change the dimension of the matrix, or even change its type (numeric or character).