R : Copyright 2004, The R Foundation for Statistical Computing
Version 2.0.1  (2004-11-15), ISBN 3-900051-07-0

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> 
>  library(aster)
> 
>  do.chisq.test <- function(x, mu, max.bin) {
+      stopifnot(all(x >= 0))
+      xx <- seq(1, max.bin)
+      yy <- dpois(xx, mu)
+      yy[length(yy)] <- ppois(max.bin - 1, mu, lower.tail = FALSE)
+      pp <- yy / sum(yy)
+      ecc <- length(x) * pp
+      if (any(ecc < 5.0))
+          warning("violates rule of thumb about > 5 expected in each cell")
+      cc <- tabulate(x, max.bin)
+      chisqstat <- sum((cc - ecc)^2 / ecc)
+      cat("chi squared statistic =", chisqstat, "\n")
+      cat("degrees of freedom =", length(ecc) - 1, "\n")
+      cat("p-value =", pchisq(chisqstat, length(ecc) - 1, lower.tail = FALSE),
+          "\n")
+      foo <- rbind(cc, ecc)
+      dimnames(foo) <- list(c("observed", "expected"), as.character(xx))
+      print(foo)
+  }
> 
>  set.seed(42)
>  nsim <- 1e4
> 
>  mu <- 2.0
>  x <- rnzp(nsim, mu)
>  do.chisq.test(x, mu, 8)
chi squared statistic = 2.593699 
degrees of freedom = 7 
p-value = 0.9198777 
                1        2        3        4        5        6        7
observed 3088.000 3130.000 2119.000 1056.000 408.0000 137.0000 43.00000
expected 3130.353 3130.353 2086.902 1043.451 417.3804 139.1268 39.75051
                8
observed 16.00000
expected 12.68375
> 
>  mu <- 1.0
>  x <- rnzp(nsim, mu)
>  do.chisq.test(x, mu, 5)
chi squared statistic = 1.508611 
degrees of freedom = 4 
p-value = 0.825115 
                1        2        3        4        5
observed 5851.000 2872.000 970.0000 245.0000 51.00000
expected 5819.767 2909.884 969.9612 242.4903 57.89792
> 
>  mu <- 0.5
>  x <- rnzp(nsim, mu)
>  do.chisq.test(x, mu, 4)
chi squared statistic = 1.828864 
degrees of freedom = 3 
p-value = 0.6086739 
               1        2        3        4
observed 7661.00 1961.000 321.0000 51.00000
expected 7707.47 1926.868 321.1446 44.51738
> 
>  nsim <- 1e6
>  mu <- 0.05
>  x <- rnzp(nsim, mu)
>  do.chisq.test(x, mu, 4)
chi squared statistic = 1.158501 
degrees of freedom = 3 
p-value = 0.7629738 
                1        2        3        4
observed 975182.0 24418.00 397.0000 3.000000
expected 975208.3 24380.21 406.3368 5.130428
> 
>  # nsim <- 1e7
>  # mu <- 0.005
>  # x <- rnzp(nsim, mu)
>  # do.chisq.test(x, mu, 3)
> 
>  mu <- 0.5
>  xpred <- 0:10
>  save.seed <- .Random.seed
>  x <- rnzp(xpred, mu, xpred)
>  .Random.seed <- save.seed
>  my.x <- rep(0, length(xpred))
>  for (i in seq(along = xpred))
+      if (xpred[i] > 0)
+          for (j in 1:xpred[i])
+              my.x[i] <- my.x[i] + rnzp(1, mu)
>  all.equal(x, my.x)
[1] TRUE
> 
> 
>