function y=gss(a,b,er)
g=(sqrt(5)-1)/2;
x1=a+(1-g)*(a-b);
x2=a+g*(b-a);
n=0;
f1=f(x1);f2=f(x2);
while abs(x2-x1)>er
if f1<f2
b=x2;x2=x1;x1=x1+(1-g)*(b-x1);
f2=f1;f1=f(x1);
else
a=x1;x1=x2;x2=a+g*(x2-a);
f1=f2;f2=f(x2);
end
n=n+1;
end
y=(x1+x2)/2
n