can someone help me by solving this error, there are three ode wich i have to solve and plot a single graph of al three equations in one graph.

function dydt=graph(t,y)

dydt = zeros(3,1) ; %column vector

dydt(1) = 1.07*y(1)*y(1)-y(1)*y(1)*y(1)-0.17*y(1)-(0.36*y(1)*y(2))-(0.0001*sqrt(y(1)*y(3))/(1+0.2*sqrt(y(1))));

dydt(2) = y(2)*(0.06*y(1)-4.06*y(2)*y(3)-0.09);

dydt(3) = (0.000089*sqrt(y(1)*y(3)))/(1+0.2*sqrt(y(1)))-0.232*y(2)*y(3)-y(3);

end

y0=[50 100 50];

tspan=[0 100];

[t,y]=ode45(@(t,y) graph(t,y),tspan,y0)

plot(t,y)

[Torsten]

Put the last 4 lines of your code to the top and rerun.

[KALYAN ACHARJYA]

@Torsten Yes sir

[Torsten]

@KALYAN ACHARJYA

Am I too harsh ? :-)

[Rik]

Comment posted as flag by @devyanshi bansal:

can u help me with ploting same for 3-d graph as well

[devyanshi bansal]

can anyone please help with the plotting of 3-d spiral graph of the same equations

Answer 1

[Satyam]

Hi Devyanshi,

To solve the error, the code can be modified by putting the last 4 lines of code to the top as suggested previously. For plotting a 3D spiral graph, one can leverage the ‘plot3’ function of MATLAB.

Refer to the documentation of ‘plot3’ function to know about the syntax: https://www.mathworks.com/help/matlab/ref/plot3.html

Here is a code snippet demonstrating its usage:

y0=[50 100 50];
tspan=[0 100];
[t,y]=ode45(@(t,y) graph(t,y),tspan,y0);

% Plot the 3D spiral trajectory
figure;
plot3(y(:,1), y(:,2), y(:,3), 'b', 'LineWidth', 2);

Warning: Imaginary parts of complex X, Y, and/or Z arguments ignored

grid on;
xlabel('y_1'); ylabel('y_2'); zlabel('y_3');
title('3D Spiral Trajectory of the ODE System');
view(3); % Set default 3D view

●

function dydt=graph(t,y)
dydt = zeros(3,1) ; %column vector 
dydt(1) = 1.07*y(1)*y(1)-y(1)*y(1)*y(1)-0.17*y(1)-(0.36*y(1)*y(2))-(0.0001*sqrt(y(1)*y(3))/(1+0.2*sqrt(y(1))));
dydt(2) =  y(2)*(0.06*y(1)-4.06*y(2)*y(3)-0.09);
dydt(3) = (0.000089*sqrt(y(1)*y(3)))/(1+0.2*sqrt(y(1)))-0.232*y(2)*y(3)-y(3);
end