The LP procedure treats missing values as missing in all rows except those that identify either upper or lower bounds on structural variables. If the row is an upper-bound row, then the type identifier is 'UPPERBD' and the LP procedure treats missing values as . If the row is a lower-bound row, then the type identifier is 'LOWERBD' and the LP procedure treats missing values as 0, except for the variables that are identified as 'UNRSTRT'.