Question

I have some measurement data which I want to plot. I plot only the points and used the Curve Fitting Toolbox to generate a regression function which I plot.

Now I want to calculate and plot the tangent on a certain point. How can I do that using Matlab?

Answer 1

If you have point and function, you can calculate the tangent which is:

let say the desired index is 5. y = mx+n

m = (diff(y) ./ diff(y)) (5)
n = y(5)-x(5)*m

and then

hold on

plot (x, (m*x+n));

links:

http://www.kxcad.net/cae_MATLAB/toolbox/curvefit/bqxox7w.html
http://www.weizmann.ac.il/matlab/toolbox/curvefit/cfit.html
http://www.mathworks.com/matlabcentral/newsreader/view_thread/170100