central difference method

Question

abdulhadi khalifa 2012-4-18

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https://ww2.mathworks.cn/matlabcentral/answers/35833-central-difference-method

编辑： Muhammad Hammad Malik 2021-2-16

How can I calculate the central difference for set of data using matlab If I have big data.Could any one help me to do it for this small data so I can I apply to my data X 0.225 0.30 0.35 0.40 0.45 0.475 Y 0.251 0.90 2.02 3.63 7.2 9.800

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Answer 1

Jan 2012-4-18

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https://ww2.mathworks.cn/matlabcentral/answers/35833-central-difference-method#answer_44866

在 MATLAB Online 中打开

You can simply use:

gradient(X, Y)

Then the first and the last element are forward and backward differences respectively. But all interior elements are central differences.

For large data sets FEX: DGradient is faster (10 to 16 times) than Matlab's gradient. In addition it can calulate the 2nd order approximation, when X is not uniformly distributed.

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Jan 2021-2-15

在 MATLAB Online 中打开

t  = linspace(0, 2*pi, 1000);
x  = sin(t);
dx = (x(11:5:end) - x(1:5:end-10)) / (10 * diff(t(1:2)));
plot(t(1:5:end-5), cos(t(1:5:end-5)), 'ro');
hold on
plot(t(5:5:end-10),dx)

Muhammad Hammad Malik 2021-2-15

编辑：Muhammad Hammad Malik 2021-2-16

@Jan thanks for the kind response. i have checked your code, but unable to understand well. why you use 11:5 and cos.

pls see what i have done, i am attaching here, the issue is i am unable to add window overlap.I also can change the window size to bigger or smaller, not restricted to use just 10.

The one you mentioned is working but how i can plot that with my time vector "IMU_ULISS.time" (1x25805), and i changed this time vector to plot mine as you can see.

Grad =gradient(Data_filtered(1:window:end),window)

figure;

plot(IMU_ULISS.time(1:window:end),Grad)

time_modified=IMU_ULISS.time(1:window:end)

hold onplot(time_modified(ceil(find(IMU_ULISS.step_instant_target(1,:)>0)/window)),Grad(ceil(find(IMU_ULISS.step_instant_target(1,:)>0)/window)),'r');

hold on

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Answer 2

abdulhadi khalifa 2012-4-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/35833-central-difference-method#answer_44873

I want to calculate the slope by this method for y and X how I can do it

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Jan 2012-4-18

The output of GRADIENT *is* the slope. See my former answer.

It would be more helpful if you reply to the different ideas you got in your other postings concerning this problem. Simply posting the problem repeatedly in new threads wastes the time of all who want to assist.

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