pgamma() & pchisq() are not always "cadlag": fix docu thanks to Robert Schlicht`s PR#18888

git-svn-id: https://svn.r-project.org/R/trunk@88402 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: maechler

src/library/stats/man/Chisquare.Rd

@@ -1,6 +1,6 @@
 % File src/library/stats/man/Chisquare.Rd
 % Part of the R package, https://www.R-project.org
-% Copyright 1995-2019 R Core Team
+% Copyright 1995-2025 R Core Team
 % Distributed under GPL 2 or later
 
 \name{Chisquare}
@@ -31,7 +31,10 @@ rchisq(n, df, ncp = 0)
   \item{ncp}{non-centrality parameter (non-negative).}
   \item{log, log.p}{logical; if TRUE, probabilities p are given as log(p).}
   \item{lower.tail}{logical; if TRUE (default), probabilities are
-    \eqn{P[X \le x]}, otherwise, \eqn{P[X > x]}.}
+    \eqn{P[X \le x]}, otherwise, \eqn{P[X > x]}, unless for \code{df=0} and
+    when \code{ncp} is missing, where the central chi-square cdf is based
+    on \code{\link{pgamma}()}; in this case, probabilities are
+    \eqn{P[X < x]} when \code{lower.tail} is true, and \eqn{P[X \ge x]}, otherwise.}
 }
 \value{
   \code{dchisq} gives the density, \code{pchisq} gives the distribution

src/library/stats/man/GammaDist.Rd

@@ -1,6 +1,6 @@
 % File src/library/stats/man/GammaDist.Rd
 % Part of the R package, https://www.R-project.org
-% Copyright 1995-2020 R Core Team
+% Copyright 1995-2025 R Core Team
 % Distributed under GPL 2 or later
 
 \name{GammaDist}
@@ -35,7 +35,8 @@ rgamma(n, shape, rate = 1, scale = 1/rate)
   \item{log, log.p}{logical; if \code{TRUE}, probabilities/densities \eqn{p}
     are returned as \eqn{log(p)}.}
   \item{lower.tail}{logical; if TRUE (default), probabilities are
-    \eqn{P[X \le x]}, otherwise, \eqn{P[X > x]}.}
+    \eqn{P[X < x]}, otherwise, \eqn{P[X \ge x]} (exceptionally not
+    \emph{cadlag} here, to ensure, e.g., \code{pgamma(0, shape=0)} remains zero).}
 }
 \value{
   \code{dgamma} gives the density,
@@ -76,7 +77,7 @@ rgamma(n, shape, rate = 1, scale = 1/rate)
 }
 
   Note that for smallish values of \code{shape} (and moderate
-  \code{scale}) a large parts of the mass of the Gamma distribution is
+  \code{scale}) a large part of the mass of the Gamma distribution is
   on values of \eqn{x} so near zero that they will be represented as
   zero in computer arithmetic.  So \code{rgamma} may well return values
   which will be represented as zero.  (This will also happen for very