If f has been defined earlier then it is possible to write a:=f(1.2,3.1);
Then a has the value of f at x=1.2 and y=3.1 .
It is also allowed to do
x1:=1.2;
y1:=1.6;
a:=f(x1,2*y1);
save('a.dta',a);
Remark: Recall that ,a being a scalar, its value is appended to the
file a.dta.