[R] nls error regarding numerics vs logicals

[Jim Bouldin]

I am trying to perform an nls for a valid negative exponential function:

zz=nls(y~constant+a.est*2.7183^(b.est*x),start=list(constant=4.0,a.est=-4,b.est
= -.005),trace=T)

and am getting a number of different error messages, the most problematic
of  which is "Error in nls(ring.area ~ constant + a.est * 2.7183^(b.est *
ba.beg), start = list(constant = 4,  : 
  REAL() can only be applied to a 'numeric', not a 'logical'"

I can't see where there are any "logicals" in this equation to cause this
problem.  Any help appreciated. Thank you.

Jim Bouldin