[Rd] What should dnorm(0, 0, -Inf) return?

[Wang Jiefei]

Good question, I cannot speak for R's developers but I would like to
provide some information on the problem. Here are the first few lines of
the dnorm function located at src\nmath\dnorm.c:

```
double dnorm4(double x, double mu, double sigma, int give_log)
{
#ifdef IEEE_754
    if (ISNAN(x) || ISNAN(mu) || ISNAN(sigma))
return x + mu + sigma;
#endif
    if(!R_FINITE(sigma)) return R_D__0;
    if(!R_FINITE(x) && mu == x) return ML_NAN;/* x-mu is NaN */
    if (sigma <= 0) {
    if (sigma < 0) ML_ERR_return_NAN;
        /* sigma == 0 */
        return (x == mu) ? ML_POSINF : R_D__0;
    }
    ....
}
```

You can clearly see where the problem is. I think either the document or
the code needs a modification.

Best,
Jiefei

On Sat, Dec 7, 2019 at 5:05 PM Weigand, Stephen D. via R-devel <
r-devel using r-project.org> wrote:

> Hi,
> Apropos of a recent Inf question, I've previously wondered if dnorm "does
> the right thing" with
>
>   dnorm(0, 0, -Inf)
>
> which gives zero. Should that be zero or NaN (or NA)?
>
> The help says "'sd < 0' is an error and returns 'NaN'" and since -Inf < 0
> is TRUE, then... is this a bug?
>
> Thank you,
> Stephen
> Rochester, MN USA
>
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