Hello,    I am new to SAS and also using PROC OPTMODEL for the first time. I am trying to do unit commitment of generators.  I have loads from hour 1 to 24.  In a particular constraint, I wish to assign the next state of a variable based on a condition.  Code :  con count{i in PLANTS, j in HOUROP}: if sum{i in PLANTS, j in HOUROP} use_plant[i,j] < pl_minup[i] then use_plant[i,j+1] = 1;   However, since my loads (j in HOUROP) has values from only 1 to 24, the following error appears  Error:  ERROR: The array subscript 'use_plant[1,25]' is invalid at line 217 column 68. ERROR: The array subscript 'use_plant[2,25]' is invalid at line 217 column 68.   I need to limit this constraint to work only till hour =23. I am finding trouble in doing so. Would appreciate any kind of help.  Thank you! ... View more