PIB -> 93 al 97 con proyección al 98,99, 2000

pib=[1.460 1.660 1.772 1.835 2.008 ]'
n=length(pib)
p1=[0;pib(1:n-1)]
p2=[0;0;pib(1:n-2)]
x=[p1 p2]
b=inv(x'*x)*(x'*pib)
s=poly(0,'s')
s=s^2-b(1)*s-b(2)
raiz=roots(s)
t=[1:n]'
x1=exp(raiz(1)*t)
x2=exp(raiz(2)*t)
x=[x1 x2]
A=inv(x'*x)*(x'*pib)
z=A(1)*x1+A(2)*x2
plot(t,pib)
t=[1:n+3]';
z1=exp(raiz(1)*t)
z2=exp(raiz(2)*t)
z=A(1)*z1+A(2)*z2
plot(t,z)