how can i plot the difference of two different plots?

clear
clc
a = 7000000; %7000km
e = 0.01;
tol = 10e-12;
tweek = 604800;
n = sqrt((3.986012e14)/(a^3));
i = 1;
t=zeros(1,tweek/60);
t(i)=0;
p = a*(1-e^2);

while (i <tweek/60)

      M = n * t(i);
      E = kepler (M, e, tol);
      v = 2*atan ( (sqrt((1+e) / (1-e)))*tan(E/2) );
      r(i) = p / (1 + e*cos(v));   
      i = i+1;
      t(i)=t(i-1)+60;
  end
  M = n * t(i);
  E = kepler (M, e, tol);
  v = 2*atan ( (sqrt((1+e) / (1-e)))*tan(E/2) );
  r(i) = p / (1 + e*cos(v)); 

%position vs time
figure;
plot (t,r)

x0 = zeros(6,1);

x0(1) = 5.047068033439438e6;
x0(2) = 3.680670525302932e6;
x0(3) = 3.000778024113080e6;
x0(4) = -4.709914732434172e3;
x0(5) = 1.797919411934430e3;
x0(6) = 5.716421195462119e3;

tspan = 0 : 60 : 604800;

options = odeset('RelTol', 1e-12, 'Abstol', [1e-12 1e-12 1e-12 1e-12 1e-12 1e-12]);

[T,X] = ode45(@twobodyprob, tspan, x0, options);

%position vs time
[m,n] = size(T);
figure;
plot(T,X(:,1), '-', T,X(:,2), '-', T,X(:,3), '.')

Answer 1

[Artur M. G. Lourenço]

for me show this:

??? Undefined function or method 'kepler' for input arguments of type 'double'.

>> help kepler

kepler not found.

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