Plot Y derivative and find resulting X value minimum
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Gavin Seddon
il 23 Nov 2015
Commentato: Star Strider
il 3 Mag 2016
, 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
il 23 Nov 2015
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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Star Strider
il 3 Mag 2016
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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