# Draw a tangent line with a given slope in Log scale

3 views (last 30 days)
Mohiedin Bagheri on 10 Sep 2021
Edited: Mohiedin Bagheri on 12 Sep 2021
Dear all,
I have a graph datapoints loaded in MATLAB. Y axis is Voltage (E) and x-axis is in Log scale. I have to draw a tangent line to this curve with a given of 50 V/dec in MATLAB. I also need to find the point where the tangent line crosses the curve. I appreciate that if someone could help.

Sulaymon Eshkabilov on 10 Sep 2021
To compute the tangent line of this curve, I would do the followings:
(1) Get the numerical data of the curve (shown in your plotted Figure)
(2) Find the polynomial (quadratic) fit model E(x) formulation using, e.g.: fit() or polyfit() or ...
(3) Take a symbolic derivative of E(x) formulation => dE(x)
(4) Compute dE(50) and E(50)
(5) Plug in the computed values in step 5 into this equation: y = dE(50)*(x-50) + E(50). This would be the tangent line equation for that point of x = 50.
(6) Plot the found tangent line data along with the original curve data.
##### 3 CommentsShow 1 older commentHide 1 older comment
Image Analyst on 12 Sep 2021
@Mohiedin Bagheri, make it easy for people to help you not hard. That means first reading the posting guidelines:
and then secondly, you will then know that you were supposed to attach your data. Don't force people to make code to somehow create data similar to yours when you already have it. Just attach your variable in a .mat file with the paperclip icon.
Mohiedin Bagheri on 12 Sep 2021
@Sulaymon Eshkabilov attached is my .m file data. Thank you