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3 results for “from:Timothy R. Johnson”

nls error control
Timothy R. Johnson · Apr 17, 2002 · r-help

I'm running a simulation that uses nls on each run. Sometimes, not unexpectedly, nls doesn't return parameter estimates (e.g., "singular gradient" error). Of course when this happens the simulation (in a loop) stops and no results are...

Monotonic regression in R??
Timothy R. Johnson · Mar 4, 2001 · r-help

I wrote an isotonic regression function for S-PLUS (kindly revised by Bill Venables). It allows for weights and three different approaches to resolving ties. It uses a non-negative least squares solution rather than the "pool adjacent violators" algorithm...

tetrachoric correlations
Timothy R. Johnson · Mar 15, 2001 · r-help

I have a function that I wrote for R to compute tetrachoric/polychoric correlations via maximum likelihood. It is given below. I have not tested it extensively but it seems to work. It could probably be cleaned-up a bit...

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