search for: rissues

Displaying 15 results from an estimated 15 matches for "rissues".

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2009 Mar 05
3
Time Series - ARIMA differencing problem
Hi, I have been using this website ( http://www.stat.pitt.edu/stoffer/tsa2/Rissues.htm http://www.stat.pitt.edu/stoffer/tsa2/Rissues.htm ) to help me to fit ARIMA models to my data. At the moment I have two possible methods to use. Method 1 If I use arima(ts.data, order=c(1,2,0), xreg=1:length(ts.data)) then the wrong value for the intercept/mean is given (checked on SPSS and...
2009 Feb 25
1
Problems with ARIMA models?
...where they report problem with ARIMA models in R. I run the examples there and they give result as shown on the website. Does this mean that nothing has corrected in R? Maybe you not have seen the page, but the author said he contacted you. Here is the URL: http://www.stat.pitt.edu/stoffer/tsa2/Rissues.htm I like to know your opinion. Mvh. Marie [[alternative HTML version deleted]]
2009 Feb 25
1
Problems with ARIMA models?
...where they report problem with ARIMA models in R. I run the examples there and they give result as shown on the website. Does this mean that nothing has corrected in R? Maybe you not have seen the page, but the author said he contacted you. Here is the URL: http://www.stat.pitt.edu/stoffer/tsa2/Rissues.htm I like to know your opinion. Mvh. Marie [[alternative HTML version deleted]]
2006 Jul 26
1
arima() function - issues
...ghlights discrepancy in "arima" function while dealing with differenced time series. Is there a substitute function similar to "sarima" mentioned in the following website implemened in R? Any pointers would be of great help. http://lib.stat.cmu.edu/general/stoffer/tsa2/Rissues.htm Thanx in advance. Sachin --------------------------------- [[alternative HTML version deleted]]
2013 Jul 18
1
Difference between arima(1, 1, 1) of y and arima(1, 0, 1) of diff(y)
Dear all, When I run an arima(1,1,1) on an I(1) variable, y, I get different estimates to when I first difference the variable myself, e.g y2<-diff(y), and then run arima(1,0,1) on y2. Shouldn't these two approaches give the same output? Any help will be much appreciated. george
2008 Mar 05
1
Need help for calculating cross-correlation between 4 multivariate time series data
Hi all, I would like to know whether there is any function in R were i can find the cross-correlation of two or more multivariate (time series) data. I tried the function ccf() but it seems like to have two univariate datasets. Please let me know. sincerely, sandeep -- Sandeep Joseph PhD Post Doctoral Associate Center for Tropical & Emerging Global Diseases Paul D. Coverdell Center,
2009 Mar 08
0
ARIMA second order differencing problem
Hi, I have been using this site ( http://www.stat.pitt.edu/stoffer/tsa2/Rissues.htm) to help me with some ARIMA modelling in R. Unfortunately the methods mentioned do not appear to work with second order differencing; arima(*, 2, *). I have used some dummy data to illustrate my point. When I use the xreg=... method, the estimate of intercept is *way* off. This can be seen b...
2009 Nov 09
0
ARIMA, xreg and intercepts
David Stoffer describes some challenges with R's output when fitting ARIMA models for different orders (see Issue 2 at http://www.stat.pitt.edu/stoffer/tsa2/Rissues.htm). R doesn't fit an intercept in the model if there is any differencing. David describes a workaround using the xreg parameter to force R to calculate an intercept. Assume I have a variable y and 3 explanatory variables a, b and c. No intercept would be produced for the model .... fit = a...
2011 May 08
1
ARMA
Hello,Could somebody tell me what is the difference between  theese 3 calls of functionsarma(x,order=c(1,0)), arima(x,order=c(1,0,0)) ar(x,order=1)?I expected same residuals of theese three models,but unexpectably for the first two R requiredinitial value of something (what?)...Thanks in advance!  [[alternative HTML version deleted]]
2011 Jun 30
0
CCF of two time series pre-whitened using ARIMA
...time series that I would like to correlate but as they are autocorrelated, I am "pre-whitening" them first by fitting ARIMA models, then correlating their residuals....as described in https://onlinecourses.science.psu.edu/stat510/?q=node/75 However, http://www.stat.pitt.edu/stoffer/tsa2/Rissues.htm discusses some issues with ARIMA in R. In particular, for issue 2, if there is any differencing, a constant term is not included, but the solution is to 1) input a series that has already been differenced and not include an order for differencing in the function, or 2) include an xreg argument....
2006 Apr 03
0
Problems with arima function (PR#8743)
I have written before, but to no avail. I have found two minor problems with fitting time series models with R. The thing is, they may be solved with MINOR adjustments to the code. I have posted these problems with detailed examples here: http://www.stat.pitt.edu/stoffer/tsa2/Rissues.htm Briefly, the problems are (1) When fitting time series models when there is an AR term present, the output says it's giving you the estimate of the intercept, when, in fact, it's giving you the estimate of the mean. These are NOT the same when an AR term is present. This occurs in...
2009 Apr 22
1
arima
Hi, I have a suggestion for the fonction arima and arima0. I think you should not call the constant an intercept because it creates confusion. It is not really an intercept but a mean. For an AR(1) the intercept mu should be defined as: X(t)=mu + phi X(t-1) + e(t) What you call intercept mu is rather defined as (X(t)-mu) = phi (X(t-1)-mu)) + e(t) which is not a common way to define an
2009 Nov 16
1
ARMAX model fitting with arima
I am trying to understand how to fit an ARMAX model with the arima function from the stats package. I tried the simple data below, where the time series (vector x) is generated by filtering a step function (vector u, the exogenous signal) through a lowpass filter with AR coefficient equal to 0.8. The input gain is 0.3 and there is a 0.01 normal white noise added to the output: x <- u
2009 Jan 21
1
forecasting issue
Hello everybody! I have a problem when I try to perform a forecast of an ARIMA model produced by an auto.arima function. Here is what I'm doing: c<-auto.arima(fil[[1]],start.p=0,start.q=0,start.P=0,start.Q=0,stepwise=TRUE,stationary=FALSE,trace=TRUE) # fil[[1]] is time series of monthly data ARIMA(0,0,0)(0,1,0)[12] with drift : 1725.272 ARIMA(0,0,0)(0,1,0)[12] with drift
2008 Jan 01
0
Wish List
...ation he prefers. Many packages could make use of it if it were in the core of R including zoo, dyn, dynlm, fame and others. This would also address comments such as in ISSUE 4 on this page which is associated with a popular book on time series: http://www.stat.pitt.edu/stoffer/tsa2/Rissues.htm 8. On Windows, package build tools should check that Cygwin is in correct position on PATH and issue meaningful error if not. If you get this wrong currently its quite hard to diagnose unless you know about it. 9. Implement the R shell() and shell.exec() commands on non-Windows systems. 10....