[R] nls problem with R

[sterlesser]

the original data are
V2 =c(371000,285000 ,156000, 20600, 4420, 3870, 5500 )
T2=c( 0.3403 ,0.4181 ,0.4986 ,0.7451 ,1.0069 ,1.553)
nls2=nls(V2~v0*(1-epi+epi*exp(-cl*(T2-t0))),start=list(v0=10^7,epi=0.9,cl=6.2,t0=8.7))
after execution error occurs as below
################################################################
Error in nlsModel(formula, mf, start, wts) : 
  singular gradient matrix at initial parameter estimates
Error in nlsModel(formula, mf, start, wts) : 
  singular gradient matrix at initial parameter estimates
In addition: Warning messages:
1: In lhs - rhs :
  longer object length is not a multiple of shorter object length
2: In .swts * attr(rhs, "gradient") :
  longer object length is not a multiple of shorter object length

could anyone help me ?thansks

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