We have a new vector defined as x(0)=0 , x(1)=0 , x(2)=\beta_0 , x(3)=\beta_1 , x(4)=\beta_2 , x(5)=\beta_3 , x(6)=0 , and x(7)=0 .
We have added four new elements, which are all zero. The benefit is that we can rewrite the equation for \boldsymbol{y} , with i=0,1,\dots,5 ,
y(i) = \sum_{k=0}^{k=m-1}w(k)x(i+(m-1)-k).As an example, we have
y(4)=x(6)w(0)+x(5)w(1)+x(4)w(2)=0\times \alpha_0+\beta_3\alpha_1+\beta_2\alpha_2,as before except that we have an additional term x(6)w(0) , which is zero.
Similarly, for the fifth-order term we have
y(5)=x(7)w(0)+x(6)w(1)+x(5)w(2)=0\times \alpha_0+0\times\alpha_1+\beta_3\alpha_2.The zeroth-order term is
y(0)=x(2)w(0)+x(1)w(1)+x(0)w(2)=\beta_0 \alpha_0+0\times\alpha_1+0\times\alpha_2=\alpha_0\beta_0.