Displaying 3 results from an estimated 3 matches for "negexp".
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2002 Mar 13
2
MASS Library
Hi,
I was just trying out an example on Page 247 of the MASS (Modern Applied
Statistics with S-plus) book and saw the function "negexp.ival".
It says it is supplied in the MASS library, however when I load the
library in R and typed:
negexp.ival
it says:
Error: Object "negexp.ival" not found
Does it mean it only appears in the MASS library for S-plus?
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2004 Apr 14
4
Non-Linear Regression Problem
...do it) to start the
Newton-Gauss Linearization least squares method when i have NO prior
information about the parameter.
W. N. Venables and B. D. Ripley (2002) "Modern Applied Statistics with S",
4 th ed., page 216-7 has a topic "Self-starting non-linear regressions"
using negexp.SSival - but i can not solve my hypothetical problem using
that - my problem is :
Y = EXP(-(THETA * t)) with data below for estimating THETA:
t Y
1 0.80
4 0.45
16 0.04
Whatever i could do, is in http://www.angelfire.com/ab5/get5/nonlinear.PDF
Any response / help / comment / suggestion /...
2002 Mar 19
0
MASS Book Exercise
...ing the same technique on using a negative exponential model
(as suggested in Exercise 1), and trying to get a confidence interval.
What I have changed is follows:
expn <- function(b0, b1, th, x) {
temp <- exp(-x/th)
model.func <- b0 + b1 * temp
# Differentiate temp
derive.negexp <- (x * temp) / th^2
Z <- cbind(1, temp, derive.negexp)
dimnames(Z) <- list(NULL, c("b0","b1","th"))
attr(model.func, "gradient") <- Z
model.func
}
wtloss.gr <- nls(Weight ~ expn(b0, b1, th, Days),
data = wtlos...