Solving Equations in MATLAB

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trythisone noone
trythisone noone am 27 Dez. 2020
Kommentiert: Ameer Hamza am 28 Dez. 2020
Hello,
I have the following equation.
cos(x) == 0
I want to get two or more possible solutions for the above equation which are 90, 270, and so on. The solve function returns the first solution only.
This technique is important for me to calculate the antenna beamwidths. Any ideas?
Thanks in Adv

Akzeptierte Antwort

Ameer Hamza
Ameer Hamza am 27 Dez. 2020
Bearbeitet: Ameer Hamza am 27 Dez. 2020
There is no general solution to such a problem. A common way is to specify several starting points for the numerical solver and find the unique solutions.
y = @(x) cos(x);
x_range = 0:0.1:4*pi;
y_sol = zeros(size(x_range));
for i = 1:numel(x_range)
y_sol(i) = fzero(y, x_range(i));
end
y_sol = uniquetol(y_sol)
  2 Kommentare
trythisone noone
trythisone noone am 27 Dez. 2020
Wow, Nice trick man. It works fine. <3
Ameer Hamza
Ameer Hamza am 28 Dez. 2020
I am glad to be of help!

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Weitere Antworten (1)

John D'Errico
John D'Errico am 27 Dez. 2020
SOME problems can be handled to find all solutions.
syms x
>> xsol = solve(cos(x) == 0,'returnconditions',true)
xsol =
struct with fields:
x: [1×1 sym]
parameters: [1×1 sym]
conditions: [1×1 sym]
>> xsol.parameters
ans =
k
>> xsol.conditions
ans =
in(k, 'integer')
>> xsol.x
ans =
pi/2 + pi*k
So we learn the set of all solutions takes the form
x = pi/2 + pi*k
where k is an integer.
Sadly, a fully general solution to many problems will not be written so easily. But you can always try.

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