Displaying 20 results from an estimated 5000 matches similar to: "Define lm/glm object without evaluating them"
2003 Oct 28
2
Confidence ellipse for correlation
Hello,
SAS' point and click interface has the option of produce a scatterplot with a
superimposed confidence ellipse for the correlation coefficient. Since I
generally like R so much better, I would like to reproduce this in R. I've
been playing with the ellipse package. In order to have the points and the
ellipse on the same graph I've done the following.
(Load ellipse
2011 Apr 20
1
How can I 'predict' from an nls model with a fit specified for separate groups?
Following an example on p 111 in 'Nonlinear Regression with R' by Ritz &
Streibig, I have been fitting nls models using square brackets with the
grouping variable inside. In their book is this example, in which
'state' is a factor indicating whether a treatment has been used or not:
> Puromycin.m1 <- nls(rate ~ Vm[state] *
+ conc/(K[state] + conc), data = Puromycin,
2003 Oct 30
2
'nls' and its arguments
Dear R experts!
I'd to fit data by 'nls' with me-supplied function 'fcn'.
1) I'd like 'fcn' to accept arbitrary arguments, i.e. I defined it
as f(...) {<body>}. (Ok, that's not actually impotant).
2) Second, I would NOT like to supply every parameter in the formula.
To illustrate this, let's look at the last example of 'nls' help
2006 Nov 29
3
R2.4 xyplot + panel.number problem
Hi all;
I'm trying to display a 2 panel plot for the Puromycin data from R
with 2 different non-linear models fitted to each group. The problem
is that as far as I know panel.number doesn't work in the latest
version of R. Can anyone give a hint how to solve this?
Here is the code that I used before and now doesn't work
xyplot(rate ~conc| state,Puromycin,
2004 May 21
1
Buglet/omission in nls package (PR#6901)
Dear all,
I noticed the following under R 1.8.1 (when nls was still a separate
package) but the same problem occurs under R 1.9.0 (where most (all?)
of nls is now in the stats package):
> data(Puromycin)
> fm <- nls(rate~SSmicmen(conc,b0,b1), Puromycin, subset = state=="treated")
> coef(summary(fm))
NULL
The problem seems to be that summary.nls uses the name
2004 Feb 02
1
Robust nonlinear regression - sin(x)/x?
You reall have only one parameter in your model, c = a/b. You can't
identify both a and b from your model, therefore, you should fit the
linear model: lm(z ~ c* sin(x)/x)
Ravi.
----- Original Message -----
From: cstrato <cstrato at aon.at>
Date: Monday, February 2, 2004 2:28 pm
Subject: [R] Robust nonlinear regression - sin(x)/x?
> Dear all
>
> Since I did not receive any
2007 Aug 22
2
Evaluating f(x(2,3)) on a function f<- function(a,b){a+b}
Dear list
I have a function and a vector, say
f <- function(a,b){a+b}
x <- c(2,3)
I want to "evaluate f on x" in the sense of computing f(x[1],x[2]). I would like it to be so that I can write f(x). (I know I can write a wrapper function g <- function(x){f(x[1],x[2])}, but this is not really what I am looking for). Is there a general way doing this (programmatically)?
2008 Nov 03
2
standard errors for predict.nls?
Dear all,
Is there a way to retrieve standard errors from nls models? The help page tells me that arguments
such as se.fit are ignored...
Many thanks and best wishes
Christoph
--
Dr. rer.nat. Christoph Scherber
University of Goettingen
DNPW, Agroecology
Waldweg 26
D-37073 Goettingen
Germany
phone +49 (0)551 39 8807
fax +49 (0)551 39 8806
Homepage http://www.gwdg.de/~cscherb1
2005 Jul 11
2
Weighted nls
Dear R Community,
I am attempting to perform a weighted non-linear least squares fit. It has already been noted that the weights option is not yet implemented for the nls function, but no one seems to offer any suggestions for getting around this problem. I am still curious if a) anyone has code they have written which includes a weight options for nls, or b) if there is another model which
2005 Jun 20
2
Fwd: How to sample from a linear mixed model
Thanks. I wonder if there is a general way of extracting var(u) and var(e), which would be needed to simulate u and e. Clearly, one can get the estimated parameters, but is there a clever way of 'setting up' the matrices??
Best
S??ren
On 6/19/05, S??ren H??jsgaard <Soren.Hojsgaard at agrsci.dk> wrote:
> I would like to draw a sample from a linear mixed model y=Xb+Zu+e which has
2010 Nov 26
3
Calling substitute(expr, list(a=1)) when expr <- expression(a+b+c)
# The result I am after is the result after a substitution in an expression, such as
substitute(expression(a+b+c), list(a=1))
expression(1 + b + c)
# However, the way I want to do it is for a an expression "stored as a variable" as
(expr <- expression(a+b+c))
expression(a + b + c)
# a) The following does not work
(expr2 <- substitute(expr, list(a=1)))
expr
# b) - whereas this
2004 Nov 08
2
Nonlinear weighted least squares estimation
Hi there,
I'm trying to fit a growth curve to some data and need to use a weighted least squares estimator to account for heteroscedasticity in the data. A weights argument is available in nls that would appear to be appropriate for this purpose, but it is listed as 'not yet implemented'. Is there another package which could implement this procedure?
Regards,
Robert Brown
2007 Jun 07
2
Nonlinear Regression
Hello
I followed the example in page 59, chapter 11 of the 'Introduction to R'
manual. I entered my own x,y data. I used the least squares. My function has
5 parameters: p[1], p[2], p[3], p[4], p[5]. I plotted the x-y data. Then I
used lines(spline(xfit,yfit)) to overlay best curves on the data while
changing the parameters. My question is how do I calculate the residual sum
of squares.
2005 Apr 19
3
Help with predict.lm
Hi
I have measured the UV absorbance (abs) of 10 solutions of a substance at
known concentrations (conc) and have used a linear model to plot a
calibration graph with confidence limits. I now want to predict the
concentration of solutions with UV absorbance results given in the new.abs
data.frame, however predict.lm only appears to work for new "conc" variables
not new "abs"
2005 Jul 31
3
Drawing a graph with vertices and edges using tcl/tk
Dear all; I would like to draw a graph with vertices and edges, and I guess tcl/tk would be appropriate. I don't know tcl/tk but have googled for a 10-page (or so) introduction to 'getting started with tcl/tk in R' but without any luck.
- Does anyone know of the existence of such a document or any other web-based material on the subject?
- Does anyone have an (informative) piece of
2012 Nov 09
9
lm function - strange error
I am following a document teaching how to use regression and right at the
onset I get an R error. I understand that variables "conc" and "signal"
should have the same length but I am using the what R manual suggests to
drop the error and it is not cooperating. What gives? The manual says
that the default is na.ombit by the way, not that it's addition does
anything
How
2005 Jul 12
10
Computer algebra in R - would that be an idea??
>From time to time people request symbolic computations beyond what D() and deriv() etc can provide. A brief look at the internet shows that there are many more or less developed computer algebra packages freely available. Therefore, I wondered if it would be an idea to try to 'integrate' one of these packages in R, which I guess can be done in more or less elegant ways... I do not know
2005 Jun 19
1
How to sample from a linear mixed model
I would like to draw a sample from a linear mixed model y=Xb+Zu+e which has been fitted with lme(), i.e. a model y ~ N(Xb, C), where C=Z cov(u) Z' + cov(e).
I've tried to figure out how to extract C from an lme object, because that would solve my problem when also using the predict() function, but without any luck.
Can anyone help on that?
2006 Aug 29
2
lattice/xyplot: plotting 4 variables in two panels - can this be done?
Hi,
I would like to create a plot of y1,y2,y3,y4 against x for several subjects such that y1 and y2 are plotted against x in one panel and y3 and y4 against x in another panel. Thus if there are 3 subjects I should end up with 6 panels. Is there a simple way of doing so (i.e. without calling xyplot() several times, and then padding the results together)??
Regards
S?ren
2001 Dec 06
2
Contrasts in lm
Dear all,
In SAS (GLM and MIXED) estimable functions (linear functions of the
parameters) can be specified in the ESTIMATE and CONTRAST statements.
Has anyone written a similar "utility" for use in connection with lm?
Thanks in advance
S?ren H?jsgaard
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