You can't just replace any FOR loop with ARYOP; it can only do a few different calculations.
For example, if you want to multiply every number in ARRAY_A by 2, and store the results in ARRAY_B, you could use:
ARYOP #AOPMUL,ARRAY_B,ARRAY_A,2instead of:
FOR I=0 TO LEN(ARRAY_B)-1 ARRAY_B[I]=ARRAY_A[I]*2 NEXT