Derivative

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Umair Riaz
Umair Riaz 2011-10-23
回答： John 2023-8-5
Hello I am working on Emotion Recognition Project and i have extracted features they are in matrix forms and now i want to calcuate the (differential/derivative) of that matrix .... i have check many examples but didnt get much...
ex: i have a column vector then How we can calculate the derivative of that column vector....
Regards

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回答（2 个）

Image Analyst
Image Analyst 2011-10-23
Did you try the gradient() function? Or use diff()? Or convolve with [1 -1] using conv()?
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Image Analyst
Image Analyst 2011-10-24
No. Don't do that. I guess you could say it's approximate because it's quantized. But you probably don't need to worry about it. Why don't you try some of the other methods and see what kind of images they produce? Or post your image and tell us what you want to find in it?
Jan
Jan 2011-10-24
If you want to calculate the derivative, the values of x have to be measured at different times or locations. E.g. for getting d/dt it matters if the values of x are measures every second, every hour or in not equidistant time steps. For images the pixels have usually the same spatial distance, which can be assumed to be 1.0, except if you want to compare picture taken with different hardware. Now call your values "Img" to avoid confusion with the location in X-direction:
Img = [1,2,3,4,5]; x = [0,1,2,3,4];
"d(Img)/dx": dx = diff(Img) ./ diff(x);
This has 4 elements only. GRADIENT uses the more stable two-sided difference quotient for the interior points:
dx = gradient(Img, x); This has 5 elements.

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John
John 2023-8-5
clc;
syms x
f = @(x) sin(x);
x = pi/2;
h = 0.0001;
d = (f(x+h)-f(x-h)/2*h)

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