[R] modelling 4-parameter curve in R does not match data - how to proceed?

[Luigi Marongiu]

sorry, I don't get it...

On Wed, Mar 17, 2021 at 2:35 PM Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
>
> On 17/03/2021 6:59 a.m., Luigi Marongiu wrote:
> > yes, but in `rutledge` I model y as `y = (M / ( 1 + exp(-(x-m)/s)) ) +
> > B`, with x being 1:45. Isn't that the equivalent of what I fed Desmos
> > with? Tx
>
> No, it's not.
>
> Duncan Murdoch
>
> >
> > On Wed, Mar 17, 2021 at 11:31 AM Duncan Murdoch
> > <murdoch.duncan using gmail.com> wrote:
> >>
> >> On 17/03/2021 5:41 a.m., Luigi Marongiu wrote:
> >>> Hello,
> >>> I have a dataset from a polymerase chain reaction. I am using the
> >>> equation given by Rutledge
> >>> (https://pubmed.ncbi.nlm.nih.gov/15601990/) but the profile I get in R
> >>> does not match the data. I ran the same thing in Desmos and instead
> >>> the profile is correct (attached).
> >>> Why do I not get the same matching model as in Desmos? I believe the
> >>> formula in R is the same as the one in Desmos, and I am using the same
> >>> parameters.
> >>> Is there a procedure to debug models?
> >>> Thanks
> >>>
> >>> Here is the code:
> >>> ```
> >>> high <- c(120.64, 66.14, 34.87, 27.11, 8.87, -5.8, 4.52, -7.16, -17.39,
> >>>          -14.29, -20.26, -14.99, -21.05, -20.64, -8.03, -21.56, -1.28, 15.01,
> >>>          75.26, 191.76, 455.09, 985.96, 1825.59, 2908.08, 3993.18, 5059.94,
> >>>          6071.93, 6986.32, 7796.01, 8502.25, 9111.46, 9638.01, 10077.19,
> >>>          10452.02, 10751.81, 11017.49, 11240.37, 11427.47, 11570.07, 11684.96,
> >>>          11781.77, 11863.35, 11927.44, 11980.81, 12021.88)
> >>> plot(1:45, high, type = "l")
> >>> rutledge <- function(p, x) {
> >>>     m = p$half_fluorescence
> >>>     s = p$slope
> >>>     M = p$max_fluorescence
> >>>     B = p$back_fluorescence
> >>>     y = (M / ( 1 + exp(-(x-m)/s)) ) + B
> >>>     return(y)
> >>> }
> >>> desmos <- rutledge(list(half_fluorescence = 27.1102, slope = 2.76798,
> >>>                           max_fluorescence = 11839.8, back_fluorescence
> >>> = -138.864) , high)
> >>>
> >>> points(1:45, desmos, type="l", col="blue")
> >>
> >>
> >> In your calculation of desmos, you are using the Y variable for x in the
> >> formula.  Calculate it this way instead:
> >>
> >> desmos <- rutledge(list(half_fluorescence = 27.1102, slope = 2.76798,
> >>                             max_fluorescence = 11839.8, back_fluorescence
> >>    = -138.864) , 1:45)
> >>
> >> Duncan Murdoch
> >>
> >
> >
>


-- 
Best regards,
Luigi