====== Variance ======
{{tag>math}}
===== Description =====
Counting observation variance from list elements

**Source**:  PROLOG str. 198 Wydawnictwo PLJ Warszawa 1991 ISBN 83-85190-63-5
===== Download =====
Program source code: {{variance.pl}}
===== Listing =====
<code prolog>
wari(L, W) :- sred(L, Sr), rozn2(L, H, Sr), suma(H, Suma, 0, Ilosc, 0),
W is Suma/Ilosc.
rozn2([], [], _).
rozn2([H|T], [R|T1], Sr) :- R is (H - Sr)*(H - Sr), rozn2(T, T1, Sr).

test :- wari([1, 2, 3, 4, 5]).</code>
===== Comments =====