how to take the derivative of the function saved from curve fitting tool

I want to take the derivative of the following function after extracting the curve fitted from cftool. I have saved the curve fitted curve to my workspace.

I want to know how to get the highest slope (derivate) of the curve with respect to x-data ?

Answer 1

[Simon Allosserie]

If you have the values of your fitted curve saved, you can calculate the first derivative by using the gradient function: https://nl.mathworks.com/help/matlab/ref/gradient.html For example

fx = gradient(x) %calculate first derivative of the vector x containing your curve data.

Hope this works :)

[zein]

but i have a saved function for the fitted curve named fittedmodel(x), how can i use gradient function for my case?

[Simon Allosserie]

You can convert your data in your desired range to a vector like this:

x = [minRange:step:maxRange];
y = fittedmodel(x);

maxSlope = max(gradient(y,step))

Then you are differentiating the values of your function.

[zein]

I used the equation, but the max slope was increasing with decreasing the step until certain limit then the max slope become constant. I think that is normal, right?

[Simon Allosserie]

As per the definition of a slope, this is indeed normal. It is literally called "derivatve" because ultimately it determines the slopes over a infinitesimal x-step. So yes, once it converges to a constant value that should be right I think!