[PERFORM] optimizer parameters

[Radhya sahal]

Dear ,all 
i would to ask you about how postgresql optimizer parameters :-
1- random page cost 
2- cpu tuple cost3- cpu operator cost4- cpu index tuple cost5- effective cache 
size
play as parameters in cost estimator equation 
i imagine that cost function is the same as
f(x,y,z,....)=ax+by......
cost(cpu tuple cost,cpu operator cost,....)
can any one help me to know the equation that cost estimator used it..
My regard 
Radhya,,,,