Dear Dr. Nash,
Thank you for your kind feedback. I was able to successfully find the
starting values for the nonlinear regression model parameters, here is my
code:
#Specifying Nonlinear Regression Model
mymod <- y ~ 1/(Beta1*x1 + Beta2*x2 + Beta3*x3)
strt <- c(Beta1 = 1, Beta2 = 2, Beta3 = 3)
The cautions people have given about starting values are worth heeding. That
nlxb() does well in many cases is useful,
but not foolproof. And John Fox has shown that the problem can be tackled very
simply too.
Best, JN
On 2023-08-19 18:42, Paul Bernal wrote:
Thank you so much Dr. Nash, I
Adding one more method:
glm(y~ x1 + x2 + x3 - 1, family = gaussian(link = "inverse"), data = mydata)
will fit the exact model (including the desired error structure).
The default GLM starting values usually work OK, but it is true that
inverse-links can sometimes be more finicky than more
Dear John, John, and Paul,
In this case, one can start values by just fitting
> lm(1/y ~ x1 + x2 + x3 - 1, data=mydata)
Call:
lm(formula = 1/y ~ x1 + x2 + x3 - 1, data = mydata)
Coefficients:
x1 x2 x3
0.00629 0.00868 0.00803
Of course, the errors enter this model
Thank you so much Dr. Nash, I truly appreciate your kind and valuable
contribution.
Cheers,
Paul
El El sáb, 19 de ago. de 2023 a la(s) 3:35 p. m., J C Nash <
profjcn...@gmail.com> escribió:
> Why bother. nlsr can find a solution from very crude start.
>
> Mixture <- c(17, 14, 5, 1, 11, 2, 16,
Colleagues,
At the risk of starting a forest fire, or perhaps a brush fire, while it is
good to see that nlxb can find a solution from arbitrary starting values, I
think Paul’s question has merit despite Professor Nash’s excellent and helpful
observation.
Although non-linear algorithms can
Why bother. nlsr can find a solution from very crude start.
Mixture <- c(17, 14, 5, 1, 11, 2, 16, 7, 19, 23, 20, 6, 13, 21, 3, 18, 15, 26,
8, 22)
x1 <- c(69.98, 72.5, 77.6, 79.98, 74.98, 80.06, 69.98, 77.34, 69.99, 67.49,
67.51, 77.63,
72.5, 67.5, 80.1, 69.99, 72.49, 64.99, 75.02,
Dear friends,
Hope you are all doing well and having a great weekend. I have data that
was collected on specific gravity and spectrophotometer analysis for 26
mixtures of NG (nitroglycerine), TA (triacetin), and 2 NDPA (2 -
nitrodiphenylamine).
In the dataset, x1 = %NG, x2 = %TA, and x3 = %2
" need to determine starting (initial) values for the model parameters for
this nonlinear regression model," ...
what nonlinear regression model? Did html get stripped?
-- Bert
On Sat, Aug 19, 2023 at 12:38 PM Paul Bernal wrote:
> Dear friends,
>
> Hope you are all doing well and having a
Dear friends,
Hope you are all doing well and having a great weekend. I have data that
was collected on specific gravity and spectrophotometer analysis for 26
mixtures of NG (nitroglycerine), TA (triacetin), and 2 NDPA (2 -
nitrodiphenylamine).
In the dataset, x1 = %NG, x2 = %TA, and x3 = %2
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