i get an error in plot

% this program is used to compute power per channel versus FWM power
% and to compute channe spaing versus FWM channel
% X = third order susceptibility
% lemda = wavelength in vacuum
% c = speed og light in vacuum
% Aeff= effecive area of the optical fiber
% n= nonlinear reflective inex
% alfa = fiber loss
% D= degeneracy factor
% eff = FWM efficiency
% Leff = effctive length
x=6*10^-15;
lemda=0.5*10^-6;
c=3*10^8;
Aeff=6.4*10^-11;
n=1.48;
alfa=.0461;
eff=.05;
Leff=22*10^3;
D=3;
k=(32*(pi)^3*x)./(n^2.*lemda*c)*(Leff/Aeff)
P=eff*(D.*k).^2*(1*10^-3)^3*exp(-alfa*75)
Pdb= 10*log10(P/10^-3)
plot(x,y)
hold on
y1 = [-59.5 -61.2 -65.5 -68 -72.5 -80];
plot(x,y1,'r')

[Geoff Hayes]

nor - presumably the error message is

 Undefined function or variable 'y'.

 Error in *** (line 26)
 plot(x,y)

The local variable y needs to be defined before you try to use it. What should it be? Why is x a scalar? Why do you have many local variables but do not use them in any of the variables that you plot? Please clarify and add comments to your code where necessary.