[R] nls problem with R

[sterlesser]

ID1  ID2     t               V(t)
1	1	0	        6.053078443
2	1	0.3403	5.56937391
3	1	0.4181	5.45484486
4	1	0.4986	5.193124598
5	1	0.7451	4.31386722
6	1	1.0069	3.645422269
7	1	1.5535	3.587710965
8	1	1.8049	3.740362689
9	1	2.4979	3.699837726
10	1	6.4903	2.908485019
11	1	13.5049	1.888179494
12	1	27.5049	1.176091259
13	1	41.5049	1.176091259

The model
(1)  V(t)=V0[1-epi+ epi*exp(-c(t-t0))]
(2)  V(t)=V0{A*exp[-lambda1(t-t0)]+(1-A)*exp[-lambda2(t-t0)]}

in formula (2) lambda1=0.5*{(c+delta)+[(c-delta)^2+4*(1-epi)*c*delta]^0.5}
                  
lambda2=0.5*{(c+delta)-[(c-delta)^2+4*(1-epi)*c*delta]^0.5}
                   A=(epi*c-lambda2)/(lambda1-lambda2)

The regression rule :
for formula (1):(t<=2,that is) first 8 rows are used for non-linear
regression
epi,c,t0,V0 parameters are obtained 
for formula (2):all 13 rows of results are used for non-linear regression 
lambda1,lambda2,A (with these parameters, delta can be calculated from them)

Thanks for help
Ster Lesser

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