MATLAB: Hii, can anyone please tell me the problem in the code ?why find doesn’t give me the index of the number in theta array thanks

Question

M=3;%sites number

N=2;%particles number

U=-1;

num_of_states= nchoosek(M+N-1,N);

fock_mat=generate_fock_states(initial_vector,M,num_of_states);

theta=centerofmass(N,M,num_of_states,fock_mat)

find(theta(:,1)==-2.0944)

any(theta(:,1)==-2.0944)

• | the result I got after running|*

theta =

0

1.0472

2.0944

-1.0472

3.1416

-2.0944

ans = Empty matrix: 0-by-1

ans = 0

Answer 1

The problem is that you are testing for equality of floating point values:

https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

https://www.mathworks.com/matlabcentral/answers/69-why-does-1-2-3-1-3-not-equal-zero#answer_271

https://www.mathworks.com/matlabcentral/answers/316889-why-two-equal-numbers-are-not-equal

https://www.mathworks.com/matlabcentral/answers/41536-why-is-2-24-10-22-4-not-equal-to-0

https://www.mathworks.com/matlabcentral/answers/20830-1-0010-does-not-equal-1-0010

etc, etc, etc.

You should change your algorithm to compare the difference against a tolerance:

tol = 1e-4;
val = -2.0944;
abs(theta(:,1)-val)<tol