# linear independent set formation

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sanket neharkar am 3 Sep. 2022
Kommentiert: Bruno Luong am 5 Sep. 2022
show that {1,cost,cos2t.......cos6t} is linearly independent
using matlab code
can anyone help
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### Akzeptierte Antwort

Bruno Luong am 3 Sep. 2022
t = rand(1,7)*2*pi;
independent = rank(cos((0:6)'.*t)) == 7
independent = logical
1
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Bruno Luong am 5 Sep. 2022
t = rand(1,7)*2*pi;
independent = rank(cos(t).^((0:6)')) == 7
independent = logical
1

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### Weitere Antworten (1)

Paul am 5 Sep. 2022
A set of functions fi(t) is linearly indepenedent if the only solution to
a1*f1(t) + a2*f2(t) .... an*fn(t) = 0 (1)
is ai = 0 for all values of t.
If eqn(1) is true, then derivatives of the lhs are also zero.
Define the coefficients ai
a = sym('a',[1 7]);
Define the test eqn and its derivatives
syms t
for ii = 0:6
eqn(ii+1) = diff(sum(a.*cos(t).^(0:6)),t,ii);
end
Put the set of equations into the form M*a = 0
[M,b] = equationsToMatrix(eqn,a); % b = 0
The only way this equation has a nonzero solution for a for all values of t is if M is singular for all t. Check the determinant
simplify(det(M))
ans = It is, in general, nonzero, so the only solution for all t that satisfies (1) is ai = 0. Therefore, the functions cos(t)^n (n=0:6) are linearly independent.
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