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airwalkery2k
Posts: **2**Member

in Matlab

Hi,

I am using Matlab for a class, and unfortunately, I don't have much experience in it.

For my problem, I need to solve an ordinary differential equation using Matlab's built-in ODE45 function. Using some tutorials, I came up with the following code to solve and plot my function.

[b]function jtd

[t,x] = ode45(@dfile,[0,20],[0;0]);

plot(t,x(:,1))

title('nonlinear')

xlabel('t'), ylabel('y'), grid

function xprime = dfile(t,x)

F=13.4;

a=0.1;

xprime = zeros(2,1);

xprime(1) = x(2);

xprime(2) = F*cos(t) - a*x(2) - x(1)^3;[/b]

It works well, but I need to be able to vary F and a using a loop to get multiple plots as the two variables change. Yet I can't for the life of me figure out how to get a variable from the main function JTD into the function xprime when I call the ode45 function.

If I could figure that out, it would help me immensely in continueing my program.

I am using Matlab for a class, and unfortunately, I don't have much experience in it.

For my problem, I need to solve an ordinary differential equation using Matlab's built-in ODE45 function. Using some tutorials, I came up with the following code to solve and plot my function.

[b]function jtd

[t,x] = ode45(@dfile,[0,20],[0;0]);

plot(t,x(:,1))

title('nonlinear')

xlabel('t'), ylabel('y'), grid

function xprime = dfile(t,x)

F=13.4;

a=0.1;

xprime = zeros(2,1);

xprime(1) = x(2);

xprime(2) = F*cos(t) - a*x(2) - x(1)^3;[/b]

It works well, but I need to be able to vary F and a using a loop to get multiple plots as the two variables change. Yet I can't for the life of me figure out how to get a variable from the main function JTD into the function xprime when I call the ode45 function.

If I could figure that out, it would help me immensely in continueing my program.

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## Comments

217Member[b]F=13.4;

a=0.1;

fun=@(x,t) dfile(x,t,F,a);[/b]

[t,x] = ode45([b]fun[/b],[0,20],[0;0]);

plot(t,x(:,1))

title('nonlinear')

xlabel('t'), ylabel('y'), grid

function xprime = dfile(t,x,[b]F,a[/b])

xprime = zeros(2,1);

xprime(1) = x(2);

xprime(2) = F*cos(t) - a*x(2) - x(1)^3;

I define the function handle of dfile out of the ode45 function. In this way you can pass the parameter to the function.

Now you can make a for cicle to make different plots, for example:

F=[12.3 13.4];

a=[0.2 0.1];

for i=1:length(F)

figure();

fun=@(x,t) dfile(x,t,F(i),a(i));

...

end

I add the function figure() so that plots on different figures.

2MemberFrom here on out, it should be smooth sailing. [b]Thanks, Giug![/b]

217Member1Member