
{{alias}}( x, λ )
    Evaluates the natural logarithm of the probability mass function (PMF) for a
    Poisson distribution with mean parameter `λ` at a value `x`.

    If provided `NaN` as any argument, the function returns `NaN`.

    If provided a negative value for `λ`, the function returns `NaN`.

    Parameters
    ----------
    x: number
        Input value.

    λ: number
        Mean parameter.

    Returns
    -------
    out: number
        Evaluated logPMF.

    Examples
    --------
    > var y = {{alias}}( 4.0, 3.0 )
    ~-1.784
    > y = {{alias}}( 1.0, 3.0 )
    ~-1.901
    > y = {{alias}}( -1.0, 2.0 )
    -Infinity
    > y = {{alias}}( 0.0, NaN )
    NaN
    > y = {{alias}}( NaN, 0.5 )
    NaN

    // Negative mean parameter:
    > y = {{alias}}( 2.0, -0.5 )
    NaN

    // Degenerate distribution at `λ = 0`:
    > y = {{alias}}( 2.0, 0.0 )
    -Infinity
    > y = {{alias}}( 0.0, 0.0 )
    0.0


{{alias}}.factory( λ )
    Returns a function for evaluating the natural logarithm of the probability
    mass function (PMF) of a Poisson distribution with mean parameter `λ`.

    Parameters
    ----------
    λ: number
        Mean parameter.

    Returns
    -------
    logpmf: Function
        Logarithm of probability mass function (PMF).

    Examples
    --------
    > var mylogpmf = {{alias}}.factory( 1.0 );
    > var y = mylogpmf( 3.0 )
    ~-2.792
    > y = mylogpmf( 1.0 )
    ~-1.0

    See Also
    --------

