Duncan,
Thank you. You are correct no one answered my question , despite the fact that
several people reply to my email, until you replied. Your exclamation is quite
clear and I thank you for your kindness. I did not pursue my question any
further as I was concerned that I would be flamed.
John
On 12/12/2016 12:26 PM, John Sorkin wrote:
David,
I did read the help page. All it says is
log1p(x) computes log(1+x) accurately also for |x| << 1 (and less
accurately when x is approximately -1).
This gives me pause. Does it mean that log(x) does not give accurate
results? If log1p gives
Many thanks!
logp1(x) worked just fine.
Best,
Faradj
Skickat från min iPhone
> 12 dec. 2016 kl. 22:54 skrev peter dalgaard :
>
> And, for crying out loud... just try it with x = 1.234e-16 or so. One would
> think that the hint |x| << 1 was obvious enough.
>
> -pd
>
>> On
And, for crying out loud... just try it with x = 1.234e-16 or so. One would
think that the hint |x| << 1 was obvious enough.
-pd
> On 12 Dec 2016, at 18:26 , William Dunlap via R-help
> wrote:
>
> Print more digits of the quotient or subtract one from it and you will
Numerical accuracy in floating point math is a much broader discussion than R,
but [1] seems to summarize it reasonably well. There are whole courses on this
topic at university.
[1]
http://www.johndcook.com/blog/2010/06/07/math-library-functions-that-seem-unnecessary/
--
Sent from my phone.
> On Dec 12, 2016, at 9:26 AM, John Sorkin wrote:
>
> David,
>
> I did read the help page. All it says is
> log1p(x) computes log(1+x) accurately also for |x| << 1 (and less accurately
> when x is approximately -1).
Not true. You evidently did not run the
The problem is that 1+x does not give accurate results for small x:
> (1+1e-17) == 1
[1] TRUE
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Mon, Dec 12, 2016 at 9:26 AM, John Sorkin
wrote:
> David,
>
> I did read the help page. All it says is
>
> log1p(x)
Print more digits of the quotient or subtract one from it and you will see
the difference:
> log1p(0.01)/log(0.01+1) - 1
[1] 8.22666379463044e-11
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Mon, Dec 12, 2016 at 8:53 AM, John Sorkin
wrote:
> At the
David,
I did read the help page. All it says is
log1p(x) computes log(1+x) accurately also for |x| << 1 (and less
accurately when x is approximately -1).
This gives me pause. Does it mean that log(x) does not give accurate
results? If log1p gives more accurate values than log, why is the log
y
College Station, TX 77840-4352
-Original Message-
From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of John Sorkin
Sent: Monday, December 12, 2016 10:54 AM
To: farad...@gmail.com; r-help@r-project.org; wdun...@tibco.com
Subject: Re: [R] Log plus one transformation in R
At the
> On Dec 12, 2016, at 8:53 AM, John Sorkin wrote:
>
> At the risk of being flamed . . .
> What is the difference between log1p(x) and log(x+1)?
> The two methods appear to give the same results:
>> log1p(0.01)/log(0.01+1)
> [1] 1
> John
Read the help page
At the risk of being flamed . . .
What is the difference between log1p(x) and log(x+1)?
The two methods appear to give the same results:
> log1p(0.01)/log(0.01+1)
[1] 1
John
John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland
> Faradj Koliev
> on Mon, 12 Dec 2016 17:23:20 +0100 writes:
> Hi all, How do I perform log(x+1) in R?
> log1p_trans() from the package ”scales" doesn’t seem to
> work for me.
amazing that you did not find log1p() in base R.
log1p(x), in the base package computes log(1+x) accurately for small x (and
large).
E.g.,
> options(digits=16)
> base::log1p(1e-14)
[1] 9.95e-15
> base::log1p(1e-14) - base::log(1+1e-14)
[1] 7.992778373591124e-18
> as.numeric(log(Rmpfr::mpfr(1,precBits=1000) + Rmpfr::mpfr(1e-14,
"?log" includes documentation for "log1p" in the base package
Will that work?
Spencer Graves
On 12/12/2016 10:23 AM, Faradj Koliev wrote:
Hi all,
How do I perform log(x+1) in R?
log1p_trans() from the package ”scales" doesn’t seem to work for me.
Best,
Faradj
Faradj,
I all you need to do is
newvalue <- log(x+1)
John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology and
Geriatric Medicine
Baltimore VA Medical Center
10 North Greene Street
GRECC
Hi all,
How do I perform log(x+1) in R?
log1p_trans() from the package ”scales" doesn’t seem to work for me.
Best,
Faradj
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