Y = evalfit(F,X) evaluates the fit F for the values X.  F is a fit 
structure, as obtained by ezfit, showfit or SELECTFIT. Y is a vector 
of the same length as X, with Y(i) = F(X(i)). 
 

 
  plotsample('power'); 
  f = ezfit('power; log'); 
  x = logspace(1,3,1000); 
  hold on; plot(x,evalfit(f,x),'r-'); hold off; 
 

ezfit, showfit, fitparam. 
Published output in the Help browser 
   showdemo evalfit