Example 18.3-1 Comparing the Solution from Maple with the Approximate Solution from the Text
This follows execution of sec183.mws
>  eq2:=xA(delta)=NAz/(c*kpp); The BC from eq 18.3-11
>  NAz:=solve(eq2,NAz); A little more complicated this time. We encounter the LambertW function. 
>  simplify(%); Not much simplification. Note that the text does not find a solution for NAz.

>  ?LambertW This tells us:

The LambertW function satisfies 

  LambertW(x) * exp(LambertW(x)) = x .
>  NAzbook:=2*c*DAB/delta/(1+DAB/kpp/delta)*log(1/(1-xA0/2)); Eq. 18.3-14 gives the approximate solution for large values of kpp.
>  eq1:=NAz=N1/delta*c*DAB;
>  eq2:=NAzbook=N2/delta*c*DAB;
>  N1:=solve(eq1,N1);
>  delta:=del*DAB/kpp;
>  N1:=simplify(N1);
>  N1:=unapply(N1,del,xA0);

>  N2:=solve(eq2,N2);
>  N2:=unapply(N2,del,xA0);

>  with(plots):
>  p1:=plot(N1(del,.1),del=0...1,color=red): red is the solution in terms of the LambertW function
>  p2:=plot(N2(del,.1),del=0...1,color=blue): blue is the approximate solution from the text.
>  display({p1,p2},title="NAz*delta/(c*DAB) vs delta*kpp/DAB"); They agree quite well for xA0=0.1