functions for exercises

functions/bioassaylp.R

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+bioassaylp <- function(a,b,x,y,n) {
+
+  # unnormalized log-posterior for bioassay (assuming uniform prior)
+
+  t <- a + b*x
+  et <- exp(t)
+  z <- et/(1+et)
+
+  # ensure that log(z) and log(1-z) are computable
+  eps <- 1e-12
+  z <- pmin(z, 1-eps)
+  z <- pmax(z, eps)
+  lp <- sum(y*log(z) + (n-y)*log(1-z))
+  return(lp)
+}
+

functions/dtnew.R

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+
+
+
+
+dtnew <- function(x, df, mean=0, scale=1, ...) {
+  dt((x-mean)/scale, df=df, ...) / scale
+}