parameters estimation for a model

Hi All,

I am facing a trouble to find two parameters, named as a and b, from the following equation

y=0.5*[1.0-erf(log(a*x)/(b*sqrt(2)))]

Can anyone help me in this regard? A data file is attached herewith for your consideration.

Best Sudipta

[John D'Errico]

No file was attached. Try harder.