[R] Poisson distribution help requested

[Martin Maechler]

>>>>> "Spencer" == Spencer Graves <spencer.graves at pdf.com>
>>>>>     on Fri, 09 Jan 2004 07:32:09 -0800 writes:

    >> ppois(0:11, 2)
    Spencer>  [1] 0.1353353 0.4060058 0.6766764 0.8571235
    Spencer> 0.9473470 0.9834364 0.9954662 [8] 0.9989033
    Spencer> 0.9997626 0.9999535 0.9999917 0.9999986

    Spencer> This is the cumulative distribution function of the
    Spencer> Poisson with mean 2 at the values 0 - 11.

    Spencer> hope this helps.  spencer graves

and from Mark's "level of significance (alpha)",
I presume Mark really wants  qpois()  which computes quantiles,
i.e., the *inverse* of ppois().

    Spencer> Mark St.John wrote:

    >> Could somebody help me to understand the syntax of R's
    >> ppois function? I'm looking to calculate the cumulative
    >> probability density of an observed value (y) given the
    >> expected mean (mu) and the level of significance
    >> (alpha). I'm coming from using SAS to do this and don't
    >> recognize the descriptions of the arguments for
    >> ppois. The definitions of lambda and p as stated in the R
    >> manuals are foreign to me!

    >> Thanks, Mark