non linear equation

Hello!
I try to compute the double exponential function this code:
f<-function(cls,a,b,c,d)a*exp(cls*b)+c*exp(cls*d)

n2<-nls(proc~f(cls,a,b,c,d),data=bline,start=list(a=600,b=-.1,c=4,d=-.
1),trace=TRUE)
proc~f(cls,a,b,c,d)

but don't work!

Thanks!



On 10 April 2013 12:47, catalin roibu <catalinroibu at gmail.com> wrote:

Hello!
I try to nls and I compute a simple exponential equation, but the 
problem in nls is to anticipate the regression coefficients.


On 10 April 2013 12:19, Jorge I Velez <jorgeivanvelez at gmail.com>

Dear Catalin,

You can look at ?nls.

Alternatively, you could also consider a linear model as follows, 
where "d" is your data:

# plot your data
with(d, plot(cls, proc, las = 1))

# linear model
fit <- lm(proc ~ I(1/cls) + I((1/cls)^2), data = d)
summary(fit)

# plotting
with(d, plot(cls, proc, las = 1))
grid <- seq(min(d$cls), max(d$cls), length = 1000) points(grid, 
predict(fit, data.frame(cls = grid)), type = "l", col = 2)

HTH,
Jorge.-




 On Wed, Apr 10, 2013 at 7:01 PM, catalin roibu

 Hello all!

 I have a problem with a double exponential equation.
this are my data's>
structure(list(proc = c(1870.52067384719, 766.789388745793, 
358.701545859122, 237.113777545511, 43.2726259059654, 
148.985133316262, 92.6242882655781, 88.4521557193262, 
56.6404686159112, 27.0374477259404, 34.3347291080268, 
18.3226992991316, 15.2196612445747, 5.31600719692165, 
16.7015717397302, 16.3923389973684, 24.2702542054496, 
21.247247993673, 18.3070717608672, 2.8811892177331, 
3.18018869564679, 8.74204132937479, 7.11596966047229 ), cls = 
c(0.25, 0.5, 0.75, 1, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 
6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10)), .Names = c("proc", "cls"), 
row.names = c("0.25", "0.5", "0.75", "1", "11", "1.5", "2", "2.5", 
"3", "3.5", "4", "4.5", "5", "5.5", "6", "6.5", "7", "7.5", "8", 
"8.5", "9", "9.5", "10"), class = "data.frame") I want to compute a

proc=a*exp(b*class)+c*exp(d*class)
or
proc=a*exp(b*class)+c*class
or a power, logarithmic equation.
Is there a possibility to calculate R squared for each model?

Thank you!

--
---
Catalin-Constantin ROIBU
Lecturer PhD, Forestry engineer
Forestry Faculty of Suceava
Str. Universitatii no. 13, Suceava, 720229, Romania
office phone     +4 0230 52 29 78, ext. 531
mobile phone   +4 0745 53 18 01
                       +4 0766 71 76 58
FAX:                +4 0230 52 16 64
silvic.usv.ro

        [[alternative HTML version deleted]]

--
---
Catalin-Constantin ROIBU
Lecturer PhD, Forestry engineer
Forestry Faculty of Suceava
Str. Universitatii no. 13, Suceava, 720229, Romania
office phone     +4 0230 52 29 78, ext. 531
mobile phone   +4 0745 53 18 01
                       +4 0766 71 76 58
FAX:                +4 0230 52 16 64
silvic.usv.ro

--
---
Catalin-Constantin ROIBU
Lecturer PhD, Forestry engineer
Forestry Faculty of Suceava
Str. Universitatii no. 13, Suceava, 720229, Romania
office phone     +4 0230 52 29 78, ext. 531
mobile phone   +4 0745 53 18 01
                       +4 0766 71 76 58
FAX:                +4 0230 52 16 64
silvic.usv.ro