[R] Error using nls function

[Mark Leeds]

David: Note that your problem is linear so it looks like you can use the lm
function to estimate a, b and c. ( or as a check against what john
did ) Unless I'm missing something  which could be the case !!!!! Also, see
Bloomfield's text for a closed form solution. I think it's
called "Intro To Fourier Analysis" or something of that nature.







On Sat, Mar 27, 2021 at 4:03 PM J C Nash <profjcnash using gmail.com> wrote:

> Use nlsr::nlxb() to get analytic derivatives. Though your problem is
> pretty rubbishy --
> look at the singular values. (You'll need to learn some details of nlxb()
> results to
> interpret.)
>
> Note to change the x to t in the formula.
>
> JN
>
> > f1 <- y ~  a+b*sin(2*pi*t)+c*cos(2*pi*t)
> > res1 <- nls(f1, data=data.frame(t,y), start=list(a=1,b=0, c=1))
> Error in nlsModel(formula, mf, start, wts) :
>   singular gradient matrix at initial parameter estimates
> > library(nlsr)
> > res1n <- nlxb(f1, data=data.frame(t,y), start=list(a=1,b=0, c=1))
> > res1n
> nlsr object: x
> residual sumsquares =  28.644  on  12 observations
>     after  3    Jacobian and  4 function evaluations
>   name            coeff          SE       tstat      pval      gradient
> JSingval
> a                11.2235            NA         NA         NA  -2.473e-12
>      4.899
> b           -1.55541e-09            NA         NA         NA   1.595e-14
>  8.399e-15
> c                11.2235            NA         NA         NA  -2.473e-12
>  5.053e-16
> >
>
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