# Poisson

Generates Poisson distributed random values.

## Syntax

Fortran:

status = virngpoisson( method, stream, n, r, lambda )

C:

status = viRngPoisson( method, stream, n, r, lambda );

## Description

This function generates Poisson distributed random numbers with distribution parameter λ, where `λ∈R; λ > 0`.

The probability distribution is given by:

k∈ {0, 1, 2, ...}.

The cumulative distribution function is as follows:

## Input Parameters

Name | Type | Description
--- | --- | ---
method | FORTRAN: INTEGER, INTENT(IN) C: int | Generation method. The specific values are as follows: `VSL_METHOD_IPOISSON_PTPE` `VSL_METHOD_IPOISSON_POISNORM` See brief description of the PTPE and POISNORM methods in Table“Values of `<method>` in method parameter”.
stream | FORTRAN: TYPE (VSL_STREAM_STATE), INTENT(IN) C: VSLStreamStatePtr | FORTRAN: Descriptor of the stream state structure. C: Pointer to the stream state structure
n | FORTRAN: INTEGER, INTENT(IN) C: int | Number of random values to be generated
lambda | FORTRAN: DOUBLE PRECISION, INTENT(IN) C: double | Distribution parameter λ.

## Output Parameters

Name | Type | Description
--- | --- | ---
r | FORTRAN: INTEGER, INTENT(OUT) C: int* | Vector of n Poisson distributed random values

## Return Values

VSL_ERROR_OK, VSL_STATUS_OK
  Indicates no error, execution is successful.
VSL_ERROR_NULL_PTR
  stream is a NULL pointer.
VSL_ERROR_BAD_STREAM

  stream is not a valid random stream.

VSL_ERROR_BAD_UPDATE

  Callback function for an abstract BRNG returns an invalid number of updated entries in a buffer, that is, `< 0` or `> nmax`.

VSL_ERROR_NO_NUMBERS

  Callback function for an abstract BRNG returns 0 as the number of updated entries in a buffer.

Parent topic: Discrete Distributions