I got a blank figure while trying to plot the phase space

I got a blank figure while trying to plot the phase space of this code.

This is the function file

function dxdt = IP(t,x,B,C,D,r,z,A,K)

dxdt = zeros(4,1);

dxdt(1) = x(3);

dxdt(2) = x(4);

dxdt(3) = (z*D*exp(-z*x(1))*(2*A*exp(2*z*r)*exp(-z*x(1)))+(B*exp(z*r))*(1+exp(-(z*x(1))))+2*C)/((1-exp(-(z*x(1))))^3)+K*(x(2)-x(1));

dxdt(4) = (z*D*exp(-z*x(2))*(2*A*exp(2*z*r)*exp(-z*x(2)))+(B*exp(z*r))*(1+exp(-(z*x(2))))+2*C)/((1-exp(-(z*x(2))))^3)+K*(x(1)-x(2));

end

this is the script:

close all

D=0.02;

r=0.04;

A=2.5;

B=0.001;

z=3.0;

C=3.25;

q1=0;

q2=0;

p1=0.632;

E=0.2;

p2=sqrt(2*E- p1^2);

dt=1/5;

tspan=[10:dt:100];

K=[0 0.050 0.5 1.5];

m=length(K);

for i=1:m;

[t x]=ode45(@(t,x)IP(t,x,B,C,D,r,z,A,K(i)),[0 100],[q1 q2 p1 p2]);

figure(1)

subplot(2,2,(i))

plot(x(:,1),x(:,3),'-b',x(:,2),x(:,4),'-r ')

xlabel('q');

ylabel('p');

end

Answer 1

[VBBV]

Choose better initial conditions e.g. for q1 and q2 they are both zero

close all
D=0.02;
r=0.04;
A=2.5;
B=0.01;
z=3.0;
C=3.25;

%>>>>>>>>> choose hetter intial coditions 
q1=1;
q2=0.5;
%-->>>>>>>>>

p1=0.632;
E=0.2;
p2=sqrt(2*E- p1^2);
dt=1/5;
tspan=[10:dt:100];
K=[0 0.050 0.5 1.5];
m=length(K);
figure(1)
hold on
for i=1:m;
[t,x]=ode45(@(t,x)IP(t,x,B,C,D,r,z,A,K(i)),[0 100],[q1 q2 p1 p2]);

subplot(2,2,(i))
plot(x(:,1),x(:,3),'-b',x(:,2),x(:,4),'-r ')

end
xlabel('q');
ylabel('p');

function dxdt = IP(t,x,B,C,D,r,z,A,K)
dxdt = zeros(4,1);
dxdt(1) = x(3);
dxdt(2) = x(4);
dxdt(3) = (z*D*exp(-z*x(1))*(2*A*exp(2*z*r)*exp(-z*x(1)))+(B*exp(z*r))*(1+exp(-(z*x(1))))+2*C)/((1-exp(-(z*x(1))))^3)+K*(x(2)-x(1));
dxdt(4) = (z*D*exp(-z*x(2))*(2*A*exp(2*z*r)*exp(-z*x(2)))+(B*exp(z*r))*(1+exp(-(z*x(2))))+2*C)/((1-exp(-(z*x(2))))^3)+K*(x(1)-x(2));
end

[Dyuman Joshi]

@VBBV, there's a typo in the comment and I think the x and y label commands should be included in the loop.

[VBBV]

yes, xlabel and ylabel commands need to be present inisde the loop

[OGUNGBEMI Ezekiel]

Thanks for the assistance. the result is not producing a phase space plot.