lotka-voltter method euler

Hi,

I want to do lotka-voltter method euler

I have code but it is so slow, do not know how to add to

for loop y(i,2) y(i,1)

%%sta

a=1.2;

b=0.6;

c=0.4;

d=0.8;

e=1.0;

f=1.2;

%%R

f = @(t,y) [y(1)*(a - b*y(2))-e*y(1); y(2)*(c*y(1)-d)-f*y(2)];;

y= [2 2];

t=0;

h=0.01;

for i=1:5000

figure(2),plot(t,y(1),'b.',t,y(2),'r.'); hold on;

xlabel('time')

ylabel('populacja')

legend('x', 'y')

ylim([0 15])

xlim([0 50])

title('Lotka-Voltery')

s=f(t,y)

y=y+h*s;

t=t+h;

end

[Torsten]

Save t and y in a vector and plot outside the loop.

Answer 1

[Jan]

Running this code in each iteration is a waste of time:

 figure(2),plot(t,y(1),'b.',t,y(2),'r.'); hold on;
 xlabel('time')
 ylabel('populacja')
 legend('x', 'y')
 ylim([0 15])
 xlim([0 50])
 title('Lotka-Voltery')

Run this once outside the loop.

 figure(2)
 axes('NextPlot', 'add');  % Equivalent to "hold on"
 xlabel('time')
 ylabel('populacja')
 legend('x', 'y')
 ylim([0 15])
 xlim([0 50])
 title('Lotka-Voltery')
 y = zeros(2, 5000);  % Pre-allocate
 y(:, 1) = [2;2];
 t = zeros(1, 5000);
 for i = 2:5000
   s       = f(t(i-1), y(:, i-1));
   y(:, i) = y(:, i-1) + h * s;   % Collect all y values
   t(i)    = t(i-1) + h;          % Collect all t values
 end
 plot(t, y(1, :),'b.', t,y(2, :), 'r.');

By the way: "lotka volterra"