= Limiting MA(1) innovations coefficient
{title2=$\lambda_\infty=\theta\ (|\theta|\le1),\quad\lambda_\infty=1/\theta\ (|\theta|>1)$}
For an <MA(1)> process, the recursion $\lambda_t=\theta/(1+\theta^2-\theta\lambda_{t-1})$ has candidate limits $\theta$ and $1/\theta$. The limit in $[-1,1]$ is $\theta$ when $|\theta|\le1$ and $1/\theta$ otherwise. The limiting innovation <variance> is $\sigma^2\max(1,\theta^2)$, expressing the same <covariance> law through an invertible reciprocal representation.
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