 Each particular problem requires particular expressions for the model and its partial derivatives.A regression model is a linear one when the model comprises a linear combination of the parameters, i.e.,

where the function formula_21 is a function of formula_22.Letting formula_23 and converting putting the independent and dependent variables in matrices formula_24 and formula_25 we can can compute the least squares in the following way, note that formula_26 is the set of all data.