Displaying 20 results from an estimated 2000 matches similar to: "How to solve differential equations with a delay (time lag)?"
2004 Jun 14
1
olesolve: stepsize
Hi,
I am doing a project on the simulation of glucose metabolism based on a
pharmacokinetic modeling in which we have 4 differential equations. I did
this in R by using the odesolve package. It works very well, but I have two
questions:
Here is the odemodel function
_________________________________________________
Ogtt.Odemodel <- function(t, y, p) {
absx <- c(-60, -45, -30,
2001 Sep 11
2
Differential Equations Using R?
To whom it may concern,
I am a student at Macaleste College, and next semester Macalester
is going to offer a course for CellBio that is mainly statistically based.
For the most part the students will be using R for analysis. The problem is
there will be some simple differential equations for the students to solve.
The committee that in charge of the classes corriculam would like only to
2004 Jun 10
0
lsoda with arbitrary zero thresholds (with psuedo-solution)
Dear Hank,
Last question first: really, only you can say for sure if 4e-281 and
5e-11 are small enough; it depends on the units you measure your state
variables in. However, this strategy cannot get the state variables to
exactly 0. Obviously, you could get closer to 0.0 faster by setting the
derivatives even larger in absolute value. You may run into problems
with the solver when the
2004 Oct 04
3
Beginners problem
Hi,
I'm new to R and have a problem with a little test program (see below).
Why doesn't <<- in function rk4
assign the new value to y so that it is seen in rktest. I thought that
<<- does exactly this. But it seems that I
didn't get it right. I would be very appreciative for an explanation of
that behaviour of <<-. I know how to
write the whole thing so that it
2003 Nov 05
3
using LSODA in R
R help list subscribers,
I am a new user of R. I am attempting to use R to explore a set of
equations specifying the dynamics of a three trophic level food chain. I
have put together this code for the function that is to be evaluted by
LSODA. My equations Rprime, Cprime, and Pprime are meant to describe the
actual equation of the derivative. When I run LSODA, I do not get the
output that
2012 Dec 05
2
stiff delay differential equations
Hello List,
Can you recommend me if odeSolve can handle stiff delay differential equations
with discontinuities? Or any other package?
Best,
-m
2013 Apr 25
2
Vectorized code for generating the Kac (Clement) matrix
Hi,
I am generating large Kac matrices (also known as Clement matrix). This a tridiagonal matrix. I was wondering whether there is a vectorized solution that avoids the `for' loops to the following code:
n <- 1000
Kacmat <- matrix(0, n+1, n+1)
for (i in 1:n) Kacmat[i, i+1] <- n - i + 1
for (i in 2:(n+1)) Kacmat[i, i-1] <- i-1
The above code is fast, but I am curious about
2006 Mar 11
1
Non-linear Regression : Error in eval(expr, envir, enclos)
Hi..
i have an expression of the form:
model1<-nls(y~beta1*(x1+(k1*x2)+(k1*k1*x3)+(k2*x4)+(k2*k1*x5)+(k2*k2*x6)+(k3*x7)+(k3*k4*x8)+(k3*k2*x9)+(k3*k3*x10)+ (k4*x11)+(k4*k1*x12)+(k4*k2*x13)+(k4*k3*x14)+(k4*k4*x15)+(k5*x16)+(k5*k1*x17)+(k5*k2*x18)+(k5*k3*x19)+
2005 Nov 06
1
Problem defining a system of odes as a C library with lsoda
I have been trying to make use of the odesolve library on my
university's Linux grid - currently R version 2.0.1 is installed and
the system runs 64-bit Scientific Linux based on Redhat. I cannot seem
to get lsoda working when I define the model as a shared C library. For
example, the following snippet uses the mymod.c example bundled with
the package:
### START
rm(list=ls())
2008 Feb 01
2
the "union" of several data frame rows
Hi,
I have a question about how to obtain the union of several data frame
rows. I'm trying to create a common key for several tests composed of
different items. Here is a small scale version of the problem. These
are keys for 4 different tests, not all mutually exclusive:
id q1 q2 q3 q4 q5 q6
1 A C
2 B D
3 A D B
4 C D B D
I would like
2003 Oct 23
2
OOP like handling of lists?
Hello,
I am writing a package with a collection of several models. In order to
allow users to play interactively with the models (in contrast to
hacking lengthy scripts), I want to put all what is needed to run a
particular model into a single list object for each model.
Then there will be a collection of functions to run the model or to
modify parameters, time steps, integration method ...,
2008 Sep 16
0
FW: odesolve dynload example
HI R Gurus,
> This is my first foray into using c-code with R, so ...
> I had a look at the archives and did not find anything on this, so
> hopefully I am not doubling up.
>
I have previously used the following approach where I needed some very
small numbers/large (using Brobdingnag):
surfacewithdiff <- function(t, y, p)
{
const=p["const"]
kay
2012 May 15
2
Renaming names in R matrix
I have the following matrix:
> dat
[,1] [,2] [,3] [,4]
foo 0.7574657 0.2104075 0.02922241 0.002705617
foo 0.0000000 0.0000000 0.00000000 0.000000000
foo 0.0000000 0.0000000 0.00000000 0.000000000
foo 0.0000000 0.0000000 0.00000000 0.000000000
foo 0.0000000 0.0000000 0.00000000 0.000000000
foo 0.0000000 0.0000000 0.00000000 0.000000000
and given this:
2013 Jan 03
1
R2OpenBUGS question with differential equations
Dear All,
Currently I am running the following code:
library(stats4)
library(odesolve)
library(rgenoud)
Input<-data.frame(SUB=c(1),time=c(0.5,3,10,15),lev=c(2.05,12.08,9.02,8))
XD<-500
IT<-3
diffeqfun<-function(time, y, parms) {
if(time<=IT)
dCpdt <- (XD/IT)/parms["Vol"] -
2008 Apr 09
3
LSODA not accurate when RK4 is; what's going on?
I'm solving the differential equation dy/dx = xy-1 with y(0) = sqrt(pi/2).
This can be used in computing the tail of the normal distribution.
(The actual solution is y(x) = exp(x^2/2) * Integral_x_inf {exp(-t^2/2) dt}
= Integral_0_inf {exp (-xt - t^2/2) dt}. For large x, y ~ 1/x, starting
around x~2.)
I'm testing both lsoda and rk4 from the package odesolve.
rk4 is accurate using step
2004 Feb 05
1
Installing odesolve under MacOSX
Installing odesolve in Raqua 1.8.0 or 1.8.1 under MacOSX gives the following
message:
Warning message: Installation of package odesolve had non-zero exit status
in: install.packages(ui.pkgs, CRAN = getOption(where), lib = .libPaths()[1])
Moreover, in the source of odesolve is no makefile.
Does anyone know how to get a proper installation?
Maartje
2008 Mar 08
1
Installing odesolve package of R under Ubuntu (Debian) Linux
Bonjour,
Je cherche à installer le package odesolve du logiciel de statistique R sous
Ubuntu Linux.
C'est un package qui contient des fonctions appelant du code en Fortran.
A l'installation sous R via le shell, j'obtiens l'erreur suivante:
Hi,
I tried to install odesolve package of R under Ubuntu Linux.
But I got the following error:
ghislain@ghislain-laptop:~$ sudo R
[sudo]
2009 Oct 19
1
updating columns using other column as reference
Dear R-gurus,
Just supose I have a dara.frame that looks like
myDF<-read.table(stdin(),head=T,sep=",")
codID,namesp,k1,k2,k3,k4
1,spA,2,5,6,3
2,spB,4,5,4,6
3,spC,2,1,5,6
4,spC,5,4,3,2
5,spD,1,2,3,4
6,spE,2,4,3,1
I need to update the columns k1-k4 with the namesp, but
considering the math between Kx and codID.
My desired output must looks like:
codID,namesp,k1,k2,k3,k4
2008 Sep 16
0
lsoda( linking to GMP for big numbers from C code)
Hi R used with C-code experts,
I had a look at the archives and did not find anything on this, so
hopefully I am not doubling up.
I have previously used the following approach where I needed some very
small/large numbers (using Brobdingnag):
surfacewithdiff <- function(t, y, p)
{
const=p["const"]
kay =p["kay"]
psii=p["psii"]
2011 Jul 27
2
fitting sine wave
Dear R-helpers
?
I have 7 data points that I want to fit a continuous curve to, that should look similar to a sine wave
My data points would mark the local minima and maxima respectively.
This is what I?ve got so far. And I would keep doing so, but sadly nls() then says that it has reached the maximum number of Iterations?
?