PRO linear_function_2_x, X, A, F, pder F=A[0]+X*A[1] ; F=A[0]+X*12.5 ;Use, for example, with ; ; X=findgen(10)+1 ; Y=findgen(10)+20 ; A=[20,1] ; weights=findgen(10) ; weights(*)=1 ; yfit=curvefit(X,Y,weights,A,/noderivative,function_name='linear_function') end