optimizer's cost formulas

Hello everybody!

I'm trying to understand the the query planner's cost estimator.
I was not able to find anywhere the formulas that estimate the cost
of each operation that the optimizer produces.

I only found this for the sequential scan:
SEQ SCAN = ( cpu_tuple_cost * rows ) + ( number of pages * seq_page_cost )
where :
cpu_tuple_cost=0.01
seq_page_cost=1.0
and "rows" and "number of pages" are given in the query plan (via
EXPLAIN ANALYZE)

I am wondering where could I find the rest formulas for the rest operations
(e.g. HashAggregate, Nested Loop, Hash Join, Index Scan, Sort, etc)

I also looked at costsize.c but could not find a formula like the above
or maybe I
couldn't make sense of it

Thank you in advance!