Data must be a single matrix Y or a list of pairs X,Y. Where might be the problem?

function Predator_prey2
alpha = 0.4;
beta = 0.8;
gamma = 0.7;
delta = 1;
epsilon = 0.5;
eta = 0.9;
lambda = 0.6;

xold = 0.8;
yold = 0.8;
zold = 0.8;

tMin = 0;
tMax = 50;

tChange = 0.001;

figure;
subplot(1,2,1);
hold on;
grid on;
axis( [-0.2 2 0.1 2 0.1 2]);
title ('Populations of foxes rabbits and chickens');
xlabel ('Population of chickens');
ylabel ('Population of rabbits');
zlabel ('Population of foxes');
xs = []; ys = []; zs = []; ts = [];

subplot(1,2,2);
hold on;
axis([tMin tMax 0.5 2.2]);
title('Population');
xlabel('Time');
ylabel('Population size');

for t = tMin:tChange:tMax;
    xs = [xs, xold]; ys = [ys, yold]; zs = [zs, zold]; ts = [ts, t];
    yNew = yold+tChange*(delta-epsilon*zold);
    xNew = xold+tChange*(eta-lambda*zold);
    zNew = zold+tChange*(beta*yold-alpha*zold+gamma*xold);

      xold = xNew;
      yold = yNew;
      zold = zNew;

      if mod(t,1)==0
          subplot(1,2,1);
          plot(xs, ys, zs,'e.');

          subplot(1,2,2);
          plot(ts,xs,'f.',ts,ys,'g.',ts,zs,'h.');
          legend('Chickens','Rabbits','Foxes');

          pause(0.01);
      end
  end

I have a predator-prey problem, where I have 1 predator and 2 preys. Could you please help me, where might be problem?

[Adam]

Not if you don't give a complete error message and format your full code to make it readable!

The problem is independent of the fact you are working with predators and prey though I imagine, but until we know which line produces the error it isn't worth guessing.

[Stephen23]

@Kristyna Pospisilova: please edit your question and show us the entire error message. This means all of the red text.

Also note that I formatted your code correctly for you. In future you can do it yourself by selecting all of the code text and then clicking the {} Code button above the textbox.

Answer 1

[Star Strider]

You aren’t using the correct color arguments in your plots. See the documentation for the plot function for a list of the correct ones, and how to create your own colors.

This works:

alpha = 0.4;
beta = 0.8;
gamma = 0.7;
delta = 1;
epsilon = 0.5;
eta = 0.9;
lambda = 0.6;

xold = 0.8;
yold = 0.8;
zold = 0.8;

tMin = 0;
tMax = 50;

tChange = 0.001;

figure;
subplot(1,2,1);
hold on;
grid on;
axis( [-0.2 2 0.1 2 0.1 2]);
title ('Populations of foxes rabbits and chickens');
xlabel ('Population of chickens');
ylabel ('Population of rabbits');
zlabel ('Population of foxes');
xs = []; ys = []; zs = []; ts = [];

subplot(1,2,2);
hold on;
axis([tMin tMax 0.5 2.2]);
title('Population');
xlabel('Time');
ylabel('Population size');

for t = tMin:tChange:tMax;
    xs = [xs, xold]; ys = [ys, yold]; zs = [zs, zold]; ts = [ts, t];
    yNew = yold+tChange*(delta-epsilon*zold);
    xNew = xold+tChange*(eta-lambda*zold);
    zNew = zold+tChange*(beta*yold-alpha*zold+gamma*xold);

      xold = xNew;
      yold = yNew;
      zold = zNew;

      if mod(t,1)==0
          subplot(1,2,1);
          plot3(xs, ys, zs,'r.');
          grid on

          subplot(1,2,2);
          plot(ts,xs,'b.',ts,ys,'g.',ts,zs,'c.');
          legend('Chickens','Rabbits','Foxes');

          pause(0.01);
      end
  end

[Kristyna Pospisilova]

Thank you very much for helping. It works!!

[Star Strider]

My pleasure!