MATLAB: Size of output ode45

differential equationsif statementloopodeode45

please help me with this problem,
i want to solve ODEs many times with different value of "v2" variable,
so i use if statement to loop it, but the output of X2 look wrong especially its size (41×4)
i try 1 time solving with one value of "v2" only, it turns out size of X2 is about 6000×4
here's the code
x_extend       = zeros(121,1);
x_compress     = zeros(121,1);
v2=0;
 for i=0:1:120
    v2=v2+i;
    save input.mat
    
    t_end = 2.5;
    TSPAN = [0 t_end];                  %Solving duration
    IC    = [0; 0; 0; 0];               %Initial conditions
    [T2, X2]= ode45(@PTVP2, TSPAN, IC,options);
    a=X2(:,3)-X2(:,1);
    x_extend(i+1)   = max(a);
    x_compress(i+1)   = min(a);
    
 end

Best Answer

You are not saving values of X in each iteration
x_extend       = zeros(121,1);
x_compress     = zeros(121,1);
v2=0;
Ts = cell(121,1);
Xs = cell(121,1);
for i=0:1:120
    v2=v2+i; % is this correct??? Or do you want v2=i???
    save input.mat
    
    t_end = 2.5;
    TSPAN = [0 t_end];                  %Solving duration
    IC    = [0; 0; 0; 0];               %Initial conditions
    [T2, X2]= ode45(@PTVP2, TSPAN, IC,options);
    a=X2(:,3)-X2(:,1);
    x_extend(i+1)   = max(a);
    x_compress(i+1)   = min(a);
    Ts{i} = T2;
    Xs{i} = X2;
end
This creates cell array T2 and X2 which save results for each iteration.
Related Question