by TomDoan » Tue Jun 17, 2014 1:21 pm
As I've told a number of people who have asked about this, it's a straightforward extension of the STAR model to a multivariate setting. In fact, this uses the univariate regressions (done withNLLS) to get guess values for the multivariate regression (done with NLSYSTEM). The main reason there's a relatively thin literature with actual data is that it can be hard to get it to work properly. In this case, for instance, the spread equation fits better with a "sharp" rather than "smooth" transition, which means that the optimal value for the gamma (the scale in the logistic) is infinity and the center point can't be estimated well using non-linear least squares since the sum of squares isn't differentiable.


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