function [a b] = sal_fit(Dsal,temp)

options=optimset('TolX',1e-6,'Display','off');

k=find(~isnan(Dsal) & ~isnan(temp));
x0=[mean(Dsal(k)),0];

y=Dsal(k);x=temp(k);
x0=fminsearch('s_f',x0,options,y,x);
a=x0(1);b=x0(2);
