pmt formula description in scheduled transactions

[Ross Palmer Mohn]

What are the last two parameters passed to these formulas? What is the
"i" for in the ppmt and ipmt formulas?

pmt(periodic rate : # of periods : initial balance : ? : ?)
ppmt(periodic rate : i : # of periods : initial balance : ? : ?)
ipmt(periodic rate : i : # of periods : initial balance : ? : ?)

Are there any other formulas available for use in scheduled
transactions?

Apologies if this is covered elsewhere -- I couldn't find it.

Thanks! -RPM