In explication ''the geometric interpretation of least squares'' Typically, the number of frequency constraints is much greater than the number of design variables (filter coefficients). In these cases, we have an overdetermined system of equations (more equations than unknowns). Therefore, we cannot generally satisfy all the equations, and are left with minimizing some error criterion to find the ``optimal compromise'' solution.'
What is meant by ''constraints''
What is the relation between constraints and the number of design variables (filter coefficients).
In this case must be using a least-squares approximation.But, are there other cases when constraints less than or equal to the number of design variables?