
{{alias}}( x, λ )
    Evaluates the natural logarithm of the probability density function (PDF)
    for an exponential distribution with rate 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
        Rate parameter.

    Returns
    -------
    out: number
        Evaluated logPDF.

    Examples
    --------
    > var y = {{alias}}( 0.3, 4.0 )
    ~0.186
    > y = {{alias}}( 2.0, 0.7 )
    ~-1.757
    > y = {{alias}}( -1.0, 0.5 )
    -Infinity
    > y = {{alias}}( 0, NaN )
    NaN
    > y = {{alias}}( NaN, 2.0 )
    NaN

    // Negative rate:
    > y = {{alias}}( 2.0, -1.0 )
    NaN

{{alias}}.factory( λ )
    Returns a function for evaluating the natural logarithm of the probability
    density function (PDF) for an exponential distribution with rate parameter
    `λ`.

    Parameters
    ----------
    λ: number
        Rate parameter.

    Returns
    -------
    logpdf: Function
        Logarithm of probability density function (PDF).

    Examples
    --------
    > var mylogpdf = {{alias}}.factory( 0.5 );
    > var y = mylogpdf( 3.0 )
    ~-2.193

    See Also
    --------

