lpslot selects the slot to be use by further lp opcodes. This is the way to load and reference several analyses at the same time.
Here is a typical orc using the opcodes:
ipower init 50000 ; Define sound generator
ifreq init 440
asrc buzz ipower,ifreq,10,1
ktime line 0,p3,p3 ; Define time lin
lpslot 0 ; Read square data poles
krmsr,krmso,kerr,kcps lpread ktime,"square.pol"
lpslot 1 ; Read triangle data poles
krmsr,krmso,kerr,kcps lpread ktime,"triangle.pol"
kmix line 0,p3,1 ; Compute result of mixing
lpinterp 0,1,kmix ; and balance power
ares lpreson asrc
aout balance ares,asrc
out aout