Different models with iterations

[Girmante]

How make program with these models. I am new in programing.

[data_null__]

Don't you need another variable?  Is density Y or X?

[Girmante]

Density is Y axis,

I'm need iterations with Gauss–Newton model if this is available. I have this example, but can I to use this or similar program with liner model or other models.

proc nlin data=pplasma plots=fit;
parms alpha=2 beta=0.4 gamma=0.00075;
model conc = alpha/(gamma*(alpha-beta))*(exp(-beta*time)-exp(-alpha*time));
bootstrap / bootci; (I don't know why you don't accept those lines)
output out=predictions predicted=prediction stdp=stdp
lclm=lower95 uclm=upper95 residual=residual;
run;
proc print data=predictions;
var conc velocity prediction stdp lower95 upper95 residual;
run;

Gauss–Newton