Gov2001 October 2004

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[gov2001-l] Question For #3

by Ellen_Knebel＠ksg05.harvard.edu

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19 years, 6 months

[gov2001-l] roots of negative numbers

by allan.friedman＠gmail.com

We're a little confused about how R treats the n-roots of negative numbers. For the inverse of the Weibull, our group came up with >F^-1 = -B * [log(1-y)]^(1/a) And we noticed two things about this. First, since y will be pulled from the uniform distribution, log(1-y) will always be negative. This means that there is no real solution for any even alpha. Is this a constraint of the problem. But, more worrisome, is that I can't seem to get real numbers for odd alpha's. The code >log(.2)^(1/3) also does not return a real result. But you should be able to take a cube root of a negative number, right??? What am I overlooking? /\llan Go Sox!

19 years, 6 months

[gov2001-l] #2 still (fwd)

by olau＠fas.harvard.edu

For more hlep with plots, refer to Zelig, Chapter 5 (which was part of the reading for this week). In short: To plot a density: plot(density(X)) # density(X) returns a list of x and y coordinates To add a density line to an existing plot: lines(density(X)) Olivia. ---------- Forwarded message ---------- Date: Wed, 20 Oct 2004 12:56:49 -0700 From: modi(a)fas.harvard.edu To: olau(a)fas.harvard.edu Subject: #2 still Hey Olivia, Thanks for the help, unfortunately more questions. So a couple R questions for number 2. If i have a set of single valued data set(i.e. a bunch of numbers, NOT a bunch of coordinate pairs) and i want to see a plot of something that looks like its density, what do i do? I have used the histogram function in the past. Is there a better way to get something smoother, or a way to increase the number of intervals on the histogram? Right now, i'm plotting a histogram against the dnorm line of what you suggested in previous email and can't get them to appear on same graph, is there a way to do this? Thanks a lot. Amit

19 years, 6 months

Fw: [gov2001-l] Fw: # 2

by olau＠fas.harvard.edu

Thanks for point this out, Ian. I always get the p* q* and d* functions confused. ----- Original Message ----- From: "Ian Yohai" <yohai(a)fas.harvard.edu> To: "'Olivia Lau'" <olau(a)fas.harvard.edu> Sent: Tuesday, October 19, 2004 11:43 PM Subject: RE: [gov2001-l] Fw: # 2 > Olivia, > > We want the density, no? So wouldn't it be dnorm? > > Ian > > -----Original Message----- > From: gov2001-l-bounces(a)lists.fas.harvard.edu > [mailto:gov2001-l-bounces@lists.fas.harvard.edu] On Behalf Of > Olivia Lau > Sent: Tuesday, October 19, 2004 11:29 PM > To: gov2001 > Subject: [gov2001-l] Fw: # 2 > > Thanks for asking, Amit. > > The gaussian (true) density is the asymtotic normal > distribution > given by N(mu, sigma^2/n), as we discussed in section. mu is > the true population mean, which you know because the Binomial > distribution is a known density. And sigma^2 is the true > population variance, which you also know. > n = (5, 25, 50) (NOT N, the binomial sample size). So now you > can get the parameters for the normal distribution that you > want > to plot. > > Now to plot it, you use lines(x, y), where x is your vector of > x > coordinates and y is your vector of y coordinates. What's x? > x > is just a series of numbers and y is f(x) where f(.) is the R > function for the Normal distribution function. (It's > pnorm(...), not f(.), but you get my point.) > > In other words, after you figure out what the parameters are, > > lines(x, pnorm(x, ...)) > > > ----- Original Message ----- > From: <modi(a)fas.harvard.edu> > To: <olau(a)fas.harvard.edu> > Sent: Tuesday, October 19, 2004 11:09 PM > Subject: # 2 > > >> Hi Olivia, >> >> What's a Gaussian (true) density, and how do i plot it? >> >> Thanks, >> Amit >> > > _______________________________________________ > gov2001-l mailing list > gov2001-l(a)lists.fas.harvard.edu > http://lists.fas.harvard.edu/mailman/listinfo/gov2001-l >

19 years, 6 months

[gov2001-l] Fw: # 2

by olau＠fas.harvard.edu

Thanks for asking, Amit. The gaussian (true) density is the asymtotic normal distribution given by N(mu, sigma^2/n), as we discussed in section. mu is the true population mean, which you know because the Binomial distribution is a known density. And sigma^2 is the true population variance, which you also know. n = (5, 25, 50) (NOT N, the binomial sample size). So now you can get the parameters for the normal distribution that you want to plot. Now to plot it, you use lines(x, y), where x is your vector of x coordinates and y is your vector of y coordinates. What's x? x is just a series of numbers and y is f(x) where f(.) is the R function for the Normal distribution function. (It's pnorm(...), not f(.), but you get my point.) In other words, after you figure out what the parameters are, lines(x, pnorm(x, ...)) ----- Original Message ----- From: <modi(a)fas.harvard.edu> To: <olau(a)fas.harvard.edu> Sent: Tuesday, October 19, 2004 11:09 PM Subject: # 2 > Hi Olivia, > > What's a Gaussian (true) density, and how do i plot it? > > Thanks, > Amit >

19 years, 6 months

[gov2001-l] Gov 2001: WANTED: Adopt a Harvard Grad Student: Ellen J. Knebel, MBA, MPA

by Ellen_Knebel＠ksg05.harvard.edu

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19 years, 6 months

[gov2001-l] pset 4 typo

by aeggers＠gmail.com

Minor typo on problem set 4: The a's and b's on problem 4 should all be alpha's and beta's (or vice versa). Andy

19 years, 6 months

[gov2001-l] office hours and appointments

by king＠harvard.edu

I keep getting asked about my office hours or appointments. as you'll see more when you all start teaching, the secret of office hours is that they were not invented to make extra or special time for students; the idea of office hours is to make it possible to keep students away during all hours other than the 1-2 that are officially designated. I don't organize things that way and I'm happy to see you if you need something whenever i'm free. i'm in my office on most days. if you need to talk with me, come by. if i'm in a meeting or something, just come back. its usually better and normally easier to just come by than to try to schedule an appointment with me (unless you really need a lot of time or absolutely need to make sure I'm there). Gary

19 years, 6 months

[gov2001-l] revised #1

by olau＠fas.harvard.edu

Hi, all. A revised problem set 4 is up on the course website -- this should clarify a lot of the questions you had this weekend. The scaled inverse Chi^2 distribution is on the course web site, under section, 10_14.pdf. Yours, Olivia

19 years, 6 months

[gov2001-l] including ps files in latex

by aeggers＠gmail.com

Hello, I've had trouble getting my R-plots into my Latex documents, and wondered if anyone could share some wisdom on this. My approach has been to save the plots out of R as .ps files in the same directory where my .tex file sits, and then invoke them in the Latex code as follows: \begin{center} \includegraphics[scale=0.8]{plot1n.ps} \includegraphics[scale=0.8]{plot1pai.ps} \end{center} Nothing appears in the dvi, and in fact I think it fails to compile the rest of the file. Do the above commands assume that I'm using a particular package? Have I put the ps files in the wrong place? I could provide more detail from the latex output if necessary. Andy Eggers

19 years, 6 months

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Gov2001 October 2004