Hello SAS Community,   I am currently working on a project where I need to utilize PROC COUNTREG in SAS, particularly focusing on utilizing a weight matrix (WMAT) in a compact form. I have a WMAT with a dimension of 139,000*139,000 which is highly sparse (only 15 values per rows). I would use a matrix in a compact form to save space with three columns. The first two columns give the row and column indices for nonzero entries in the spatial weights matrix. The third column in the data set contains the nonzero entries in the spatial weights matrix. This option is already present in PROC SPATIALREG(proc spatialreg pages2355-2356 ), it is possible to adapt this feature even in PROC COUNTREG? Has anyone ever had this problem? Could anyone please provide share some insights on how to properly utilize the WMAT in a compact form within PROC COUNTREG? Any examples, tips, or resources you could share would be greatly appreciated. Thank you in advance for your assistance!   Best regards, Luca ... View more