# [R] dnorm and qnorm

Bert Gunter gunter.berton at gene.com
Sat Nov 13 00:01:36 CET 2010

```There is no "reversing the dnorm function" -- dnorm is many to one in
general (in the normal case, 2 to 1 except for the mean). How would
you "reverse" dunif, for example?!

However, with that understanding you could do a simple one dimensional
search within the range you want via optimize(), as in

> optimize(function(x)abs(dnorm(x) - .3286),lower=-5,upper = 0) ## or use squared error
\$minimum
[1] -0.6228337

\$objective
[1] 4.817833e-06

-- Bert

On Fri, Nov 12, 2010 at 2:35 PM, Edwin Sun <csun at cfr.msstate.edu> wrote:
>
> Hello all,
>
> I have a question about basic statistics.  Given a PDF value of 0.328161,
> how can I find out the value of -0.625 in R? It is like reversing the dnorm
> function but I do not know how to do it in R.
>
>> pdf.xb <- dnorm(-0.625)
>
>> pdf.xb
> [1] 0.328161
>
>> qnorm(pdf.xb)
> [1] -0.444997
>
>> pnorm(pdf.xb)
> [1] 0.628605
>
> Many thanks,
>
>
> Edwin
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/dnorm-and-qnorm-tp3040427p3040427.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
>

--
Bert Gunter
Genentech Nonclinical Biostatistics

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