Good afternoon,
I need to fit a nonlinear regression function of the form:

y = erfc[2 * sqrt(b)] * x

where erfc is complementary error function and b is the only parameter to be estimated, with the initial value b=1.

Can someone help me with the appropriate nl command? I cannot find anything under help erfc or help erf.

Thank you very much in advance!

Piotr Lewczuk