[R] fitting

[Meli Massimiliano]

Hello All,

i would fit my data with a function like this :

y = a0 + a1 * exp(-x/a2) + a3 * exp(-x/a4) + a5 * exp(-x/a6) + a7 * 
exp(-x/a8) + a9 * exp(-x/a10)

plus i have to impose that

a1 + a3 + a5 + a7 + a9 = 1

a1 , a3 , a5 , a7 , a9 >= 0

i try with nls, but i do not know how to impose the "normalization" 
restrain of the coefficient.
How i can do it with R ?

thanks a lot
max