My code won't run, related to ode function

%E_as_a_function_of_time
m = 1; % mass [kg]
k = 4; % spring constant [N/m]
c = 1; % friction coefficient [Ns/m]
omega0 = sqrt(k/m); p = c/(2*m);
y0 =0.1; v0 = 0; % initial conditions
[t,Y] = ode45(@f,[0,10],[y0,v0],omega0,[],p); % solve for 0<t<15
y = Y(:,1); v = Y(:,2); % retrieve y, v from Y
figure(1); plot(t,y,'ro-',t,v,'b+-');% time series for y and v
grid on; axis tight;
%---------------------------------------------------
function dYdt = f(t,Y,omega0,p); % function defining the DE
y = Y(1); v = Y(2);
dYdt=[ v ; -omega0^2*y-2*p*v]; % fill-in dv/dt
end

Answer 1

[David Goodmanson]

Hi Dardenella,

try the same thing only with

[t,Y] = ode45(@(t,Y) f(t,Y,omega0,p), [0,10],[y0,v0]);     % solve for 0<t<10   [not 15]

Sometimes it's less than obvious where the @'s should go. But the function call has to match the argument list it the function definition.

[Stephen23]

See also:

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html

Answer 2

[Poojana mathlab]

%mass [kg] %spring constant

k=4; %spring constant[N/m]

omega0=sqrt(k/m)

x0=0.1; v0=0 %initial conditions

[t,X]=ode45(@f,[0,10],[y0,v0],[],omega0); %solve for 0<t<10

x= X(:,1);v=X(:,2); %retrieve y,v from X

figure(1); plot(t,x,'b+-',t,v,'ro-'); %time series for x and v

%--------------------------------------

function dYdt= f(t,Y,omega0);x=X(1);v=X(2);

dYdt=[v;-omega062*x];end

doesnt work

[Stephen23]

Works perfectly, following the answer and comment above and fixing all of the mismatching variable names:

m=1;%mass [kg]
k=4;%spring constant[N/m]
omega0=sqrt(k/m);
fun = @(t,Y) f(t,Y,omega0);
[t,Y]=ode45(fun,[0,10],[0.1,0]); %solve for 0<t<10
x=Y(:,1);
v=Y(:,2);
plot(t,x,'b+-',t,v,'ro-')

%--------------------------------------
function dYdt = f(t,Y,omega0)
x=Y(1);
v=Y(2);
dYdt=[v;-omega0*x];
end