How to Help Determine the Roots of X =Tan(X), Graph Y = X And Y = Tan(X), And also plot a red circle At The Intersection Points Of The Two Curves. Please help.

clear all 
close all
clc
% %%To plot tan(theta), if you use usual plot function
% and linspace, you get a cntinuous function like this
% to use fplot, you have to initiate function
%%y=tan(x) function    theta in radians=180 deg/Pi
f=@(theta) tan(theta) %@(theta) mean f is a function on theta   
%%y=tan(x) function    theta in degrees
%f2=@(theta) tand(theta); % tand(theta) theta is in degree   
%%y=x  straight line function    theta in radians=180 deg/Pi
f3=@(theta) theta; %straight line y=x
%Plot the functions
figure
fplot(f,[-2*pi,2*pi]);
% figure
% fplot(f2,[-360,360]);
hold on
fplot(f3,f3)
ylim([0 6])
xlim([0 6])
%Note fplot have the same syntax as ezplot
%%FIND x VALUE IN THE FOLLOWING ITERATION%%%
tanxx = @(x) tan(x)-x
for a = 4:4.6
    xs = fzero(tanxx, a)
end

%I've tried to use this function 'Intersections' but could not make it work. Detect Curve Intersections, Quickly and Easily » File Exchange Pick of the Week - MATLAB & Simulink (mathworks.com)

[Steven Lord]

What does "could not make it work" mean in this context?

• Do you receive warning and/or error messages? If so the full and exact text of those messages (all the text displayed in orange and/or red in the Command Window) may be useful in determining what's going on and how to avoid the warning and/or error.
• Does it do something different than what you expected? If so, what did it do and what did you expect it to do?
• Did MATLAB crash? If so please send the crash log file (with a description of what you were running or doing in MATLAB when the crash occured) to Technical Support so we can investigate.

[juan sanchez]

I meant that the 'intersections' function did not worked for my posted code. I wanted to know how to make this function 'intersections' work and then be able to plot the roots as red circle markers on the plot.

Answer 1

[Nikhil Baishkiyar]

Have you seen the example given for the function intersections? It computes the intersection of two vectors, not two function handles. I have tried it and found the solution. You can use

x = 0:0.0001:5;
f = tan(x);
f3 = x;

I used these vectors in the same way as this example and got what you wanted.