Those are subscript reduction operators. They collapse the dimensionality of your matrix and the + tells SAS to do this by summing. If you have a matrix Z = {1 2 3, 4 5 6, 7 8 9} then Z[+,] = {(1+4+8) (2+5+8) (3+6+9)} = {12 15 18}, which is a rowvector. Z[,+] = {1+2+3,4+5+6,7+8+9} = {6,15,24}, which is a columnvector. See http://support.sas.com/documentation/cdl/en/imlug/59656/HTML/default/viewer.htm#workmatrix_sect14.htm for more info.

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