nls problem

Hello,

Tip: in a formula, pH^2 = pH*pH is an interaction.

pH^2 = pH*pH = pH + pH + pH:pH = pH

Try I(pH^2)

Hope this helps,

Rui Barradas

?s 12:07 de 02/04/20, Troels Ring escreveu:

Dear friends - I'm on Win10 with R 6.3.1 and have a very simple 
problem with
nls which apparently gives a decent fit to the parable below, even 
without
starting values. But when I then think I know the meaning of the three
parameters a, b, and d it goes very wrong. I guess I am again overlooking
something easy but cannot spot it.

BW
Troels Ring,

Aalborg, Denmark



aedf <- structure(list(Flux = c(-0.141256, -0.154709, -0.215247, 
-0.302691,

???????????? -0.32287, -0.511211, -0.605381, -0.813901, -1.11659, 
-1.76906

), pH = c(7.06273, 7.11182, 7.16182, 7.18818, 7.21455, 7.23818,

?????????? 7.26273, 7.28455, 7.31182, 7.34364)), class = "data.frame",
row.names = c(NA,

-10L))

m <- with(aedf,nls(Flux~a + b*pH + d*pH^2))


with(aedf,plot(pH,Flux))

with(aedf,lines(pH,fitted(m),lty=1,col="red",lwd=3))


m

# a??????? b??????? d

# -1630.70?? 457.67?? -32.11


fitted(m)

# 1] -0.22087053 -0.09989926 -0.13579690 -0.21936385 -0.34761742 
-0.50048799

# [7] -0.69729602 -0.90471194 -1.20692552 -1.61994657


FPG <- function(pH) -1630.70 + 457.67*pH -32.11*pH^2


FPG(aedf$pH)

# [1] -0.016359649? 0.107602395? 0.074773375 -0.007166685 -0.133786467

# [6] -0.285187665 -0.480463769 -0.686513537 -0.987013685 -1.398026917


# So why aren't fitted(m) and FPG(aedf$pH) not closer ("equal")?



This email has been scanned by BullGuard antivirus protection.
For more info visit www.bullguard.com
<http://www.bullguard.com/tracking.aspx?affiliate=bullguard&buyaffiliate=smt 

p&url=/>

????[[alternative HTML version deleted]]