Most of the mass of that distribution is within 3e-100 of 2. You have to be pretty lucky to have a point in sequence land there. (You will get at most one point there because the difference between 2 and its nearest neightbors is on the order of 1e-16.)
seq(-2,4,len=101), as used by default in curve, does include 2 but seq(-3,4,len=101) and seq(-2,4,len=100) do not so curve(..., -3, 4, 101) and curve(..., -2, 4, 100) will not show the bump. The same principal holds for numerical integration. Bill Dunlap TIBCO Software wdunlap tibco.com On Wed, Feb 10, 2016 at 6:37 PM, C W <tmrs...@gmail.com> wrote: > Dear R, > > I am graphing the following normal density curve. Why does it look so > different? > > # the curves > x <- seq(-2, 4, by=0.00001) > curve(dnorm(x, 2, 10^(-100)), -4, 4) #right answer > curve(dnorm(x, 2, 10^(-100)), -3, 4) #changed -4 to -3, I get wrong answer > > Why the second curve is flat? I just changed it from -4 to -3. There is > no density in that region. > > > Also, I am doing numerical integration. Why are they so different? > > > x <- seq(-2, 4, by=0.00001) > > sum(x*dnorm(x, 2, 10^(-100)))*0.00001 > [1] 7.978846e+94 > > x <- seq(-1, 4, by=0.00001) #changed -2 to -1 > > sum(x*dnorm(x, 2, 10^(-100)))*0.00001 > [1] 0 > > What is going here? What a I doing wrong? > > Thanks so much! > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
