dear JN,

Thanks for the reply. I will consider using the nlsr package. But for now I make did with reducing the exponent. It is working for me.

very many thanks for your time and effort....

yours sincerely,

AKSHAY M KULKARNI

________________________________

From: J C Nash <

[hidden email]>

Sent: Wednesday, March 6, 2019 10:40 PM

To: akshay kulkarni; R help Mailing list

Subject: Re: [R] Fw: inconsistency in nls output....

nls() is a Model T Ford trying to drive on the Interstate. The code

is quite old and uses approximations that work well when the user

provides a reasonable problem, but in cases where there are mixed large

and small numbers like yours could get into trouble.

Duncan Murdoch and I prepared the nlsr package to address some

of the weaknesses (in particular we try to use analytic derivatives).

The output of nlsr also gives the singular values of the Jacobian, though

I suspect many R users will have to do some work to interpret those.

You haven't provided a reproducible example. That's almost always the

way to get definitive answers. Otherwise we're guessing as to the issue.

JN

On 2019-03-06 7:48 a.m., akshay kulkarni wrote:

> dear members,

> with reference to the attached message:

>

> I think I have found out the problem:

> YLf13 has the structure:

> YLf13 <- a*exp(-1000*LM1); LM1 is another vector.

>

> most of the YLf13 vector is getting populated with zeros, I think, because of the very low value of exp(-1000*LM1). Is there any method in R wherein I can work with these very low values?

>

> Or is the problem not related to the structure of YLf13?

>

> very many thanks for your time and effort...

> yours sincerely,

> AKSHAY M KULKARNI

>

>

> ________________________________________

> From: R-help <

[hidden email]> on behalf of akshay kulkarni <

[hidden email]>

> Sent: Wednesday, March 6, 2019 6:02 PM

> To: R help Mailing list

> Subject: [R] inconsistency in nls output....

>

> dear members,

> I have the following nls output:

>

> Formula: YLf13 ~ (d + e * ((XL)^(1/3)) + f * log(LM3 + 18.81))

>

> Parameters:

> Estimate Std. Error t value Pr(>|t|)

> d 5.892e-09 8.644e-10 6.817 2.06e-11 ***

> e -6.585e-09 5.518e-10 -11.934 < 2e-16 ***

> f 1.850e-10 2.295e-10 0.806 0.42

> ---

> Signif. codes: 0 �***� 0.001 �**� 0.01 �*� 0.05 �.� 0.1 � � 1

>

> Residual standard error: 9.57e-10 on 677 degrees of freedom

>

> Number of iterations to convergence: 2

> Achieved convergence tolerance: 3.973e-08

>

> ------

> Residual sum of squares: 6.2e-16

>

> ------

> t-based confidence interval:

> 2.5% 97.5%

> d 4.195378e-09 7.589714e-09

> e -7.668142e-09 -5.501342e-09

> f -2.655647e-10 6.354852e-10

>

> ------

> Correlation matrix:

> d e f

> d 1.0000000 -6.202339e-01 -7.832539e-01

> e -0.6202339 1.000000e+00 -2.127301e-05

> f -0.7832539 -2.127301e-05 1.000000e+00

>

>

> if I let XL = 1.1070513 and LM3 = 0.3919 , and consider the coeffs as given above, the right hand side of the above equation is negative.

> But YLf13 is always positive! How is this possible? Am I interpreting the result of the nls output properly? Should I interpret the coeffs differently? I have done hours of thinking over the above problem but couldn't find any results...

>

> I cannot provide the full values of YLf13, XL and LM3 due to IPR issues....please cooperate......however, if the only way to solve the problem is to give these values, I would indeed give them.....

>

> Also forgive me if there is a minor mistake in my calculations... or a typo....

>

> very many thanks for your time and effort....

> yours sincerely,

> AKSHAY M KULKARNI

>

> [[alternative HTML version deleted]]

>

>

> ______________________________________________

>

[hidden email] mailing list -- To UNSUBSCRIBE and more, see

>

https://stat.ethz.ch/mailman/listinfo/r-help> PLEASE do read the posting guide

http://www.R-project.org/posting-guide.html> and provide commented, minimal, self-contained, reproducible code.

>

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______________________________________________

[hidden email] mailing list -- To UNSUBSCRIBE and more, see

https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide

http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.