% 
% ratecon.m - this MATLAB file illustrates the concept of the
% rate constant for the differential equation
%    N'(t) = k (Neq - N(t))
% by prompting the user to give a range of rate constants
% and an initial value and plotting the trajectories for 
% 5 rate constants over the given range
%
!c:
Neq=input('input equilibrium Neq:    ')
N0=input('input initial population N0:     ')
klo=input('input low value for rate constant k:     ')
khi=input('input high value for rate constant k:     ')
n=input('end of time interval T:     ')
x=zeros(n,1);
t=zeros(n,1);
for j=1:5
k=klo+(khi-klo)*.25*(j-1);
for i=1:n
t(i)=i-1;
x(i)=Neq-(Neq-N0)*exp(-k*t(i));
end;
plot(t,x);pause
end;
title('graph with varying k values'),pause
s=input('Do you want to stop - if so enter 0')
end