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 double exponential equation like this:
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!

-- 
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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
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