Hello all,
I am trying to fit some data using the NLINFIT of MATLAB and using SAS.
I am trying to fit the well know RICHARDS growth curve.
It looks like y=a*(1-b*exp(-c*t))^d where we want to estimate the
parameters a,b,c,and d. Here t is my input and is age squared while y
is the weight of
1-b*exp(-c*t) is negative only if b*exp(-c*t) 1, which implies
log(b) c*t, I think. Is this a reasonable circumstance in terms of
the theory that led to the Richards growth curve?
You say this occurs frequently in your data; since b and c are
presumably constants for a given data set,
