The L0F's are assigned automatically by PHOENICS at the start of the execution of the EARTH program. Their values depend upon the size of the computational grid that is being used, ie upon the values of NX, NY and NZ, and on whether PARAB and STEADY are TRUE or FALSE.
Most of the L0F's remain fixed throughout the subsequent calculation but for FFV's the L0F's are given different values for each slab. Therefore, in order to refer in GROUND to variables contained in the F-array, the user needs to be able to ascertain the values of the L0F's.
PHOENICS provides a simple means of doing so, namely the L0F(LB) function subroutine. First, however, attention will be turned to the argument of that function, namely LB.