I think the PARMS statement in GLIMMIX doesn't like parentheses. Try this PARMS statement:   PARMS .,.,., 0, 0,., 0, 0, ., ., 0, 0, ., ., . /hold=3,4,6,7,10,11; If that does not work, then I think you may have to pass the values in a dataset. Non-zero entries can be obtained by fitting a UN covariance structure to separate analyses using a BY year; statement. Note that the matrix must be a full 15x15 matrix. See the example at this link in the PLM documentation: https://documentation.sas.com/doc/en/statug/15.2/statug_plm_examples07.htm .  I realize this is getting pretty complicated.   SteveDenham   ... View more