Solving Equations in MATLAB

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trythisone noone
trythisone noone 2020-12-27
评论： Ameer Hamza 2020-12-28
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

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Ameer Hamza
Ameer Hamza 2020-12-27
编辑：Ameer Hamza 2020-12-27
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)

更多回答（1 个）

John D'Errico
John D'Errico 2020-12-27
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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