Euler's Method system of odes

Hello, I'm new to MATLAB and I'm stuck. I am trying to solve two first order ode using the Forward Eulers method. I thought my code was correct, but I think the first plots arewrong. Can someone please take a look at this?

%parametrs
A= 5;
B=50;
C=0.1;
D=1e-5;

h=0.0001;
t_final=10;
N=t_final/h;

t(1)=0;
x(1)=0;
y(1)=0;

% equations
% dx/dt = 1/D*x
% dy/dt=(1/C)*(A-(B*y)-x)

for i=1:N
    t(i+1)=t(i)+h;
    x(i+1)=(1./D)*x(i);
    y(i+1)=(1./C)*(A-(B*y(i))-x(i));
end
figure(1);clf(1)
plot(t,x)
figure(2);clf(2)
plot(t,y);

Answer 1

[Jan]

You determine the derivatives:

% dx/dt = 1/D*x
% dy/dt=(1/C)*(A-(B*y)-x)

Now x(i+1) and y(i+1) are not the values of these derivatives at the point x(i), y(i), but:

x(i+1) = x(i) + (1./D)*x(i) * h;
y(i+1) = y(i) + (1./C)*(A-(B*y(i))-x(i)) * h;

[Karol T]

Right, my fault. But still the drawing is one straight f = 0

[Karol T]

Drawing of (t,x)

[Jan]

If x starts at 0, it must sty at 0 according to the formula. y is not a straight line:

plot(t(1:100), y(1:100))