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Plot Y derivative and find resulting X value minimum

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Gavin Seddon
Gavin Seddon 2015-11-23
评论： Star Strider 2016-5-3
, I have X and Y data as time and distance. I would like to find the derivative the Y values and plot this. Therefore yielding an acceleration time graph (2nd derivative). Next it is necessary to calculate the minimum of this curve. How do I find the derivative of the entire Y column to generate the new plot and then do I calculate the minimum with fminbnd? Thank yo.

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Star Strider
Star Strider 2015-11-23
Use the gradient function to calculate the first derivative, the del2 function to calculate the second derivative, and the min function to find the minimum.
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Gavin Seddon
Gavin Seddon 2016-5-3
Hello Star Strider apologies for the long delay. I have been considering using the Z axes to show the second differential by plotting the first differential on it.
How would I take the first differential of the column Y values and append these new values into an additional column of the same table. I made then use the curve fitting tool to select the X, Y and Z axes? Gavin.
Star Strider
Star Strider 2016-5-3
No worries.
I am not certain what you want to do. If you want to plot vectors in 3D, consider the plot3 function. Use the same independent variable, then plot each vector (function, first derivative, second derivative) as function so it. (I don’t have the Curve Fitting Toolbox, so I can’t help you with its functions.)
For example:
x = ...;
y = ...;
h = mean(diff(x));
d1y = gradient(y,h);
d2y = del2(y,h);
figure(1)
plot3(x,y, x,d1y, x, d2y)
grid on
legend('Function','First Derivative','Second Derivative')
I’m not certain what you want to do, but if I were to plot them in 3D, I would use plot3.

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