how to interpolate the data over uniform time grid

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PetronasAMG on 26 Sep 2021
Answered: Nipun on 30 May 2024 at 9:27
Since numerical solution obtained from ode45 is a non uniform in time, I need to obtain the frequency power spectrim of the solution, but first, i need to interpolate the date over unifrom time grid. How would i able to do so? I am completely stuck after inputting vlause from ODE45! Please explain the steps!
function dxdt = frs(t,x)
dxdt = zeros(3,1);
dx1dt = -((4/5)*x(2)+x(1));
dx2dt = x(3) + ((4/9)*x(2));
dx3dt = (1/8)+((x(1)-2.5)*x(2));
end
tspan = [0:10:100];
xi = [1.0;4.0;2.0];
[t,x]= ode45(@frs,tspan,xi);
Walter Roberson on 26 Sep 2021
Since numerical solution obtained from ode45 is a non uniform in time
That is only the case if you pass in a two-element tspan. When you pass in a tspan that is uniform in time, the way you do, then the output from ode45 will only be at those times, and so the output would be uniform in time.
Mathieu NOE on 27 Sep 2021
you can also interpolate the output data of your ode solution over a new time vector (linear)
use interp1
maybe this will be faster than forcing ode to work on fixed , refined time vector

Nipun on 30 May 2024 at 9:27
Hi [First Name]
I understand that you want to interpolate data over a uniform time grid. Here’s how you can do it using interp1 in MATLAB:
% Given data
time = [0, 1, 4, 5, 6]; % Non-uniform time points
data = [10, 20, 15, 25, 30]; % Corresponding data points
% Uniform time grid
uniformTime = linspace(min(time), max(time), 100);
% Interpolate data over uniform time grid
uniformData = interp1(time, data, uniformTime, 'linear');
% Display results
plot(time, data, 'o', uniformTime, uniformData, '-');
xlabel('Time');
ylabel('Data');
legend('Original Data', 'Interpolated Data');
For more details on interpolation, refer to the MathWorks documentation on interp1: https://www.mathworks.com/help/matlab/ref/interp1.html
Hope this helps.
Regards,
Nipun

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