Rational power of a positive definite matrix

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Qian Feng
Qian Feng le 13 Fév 2017
Commenté : Qian Feng le 13 Fév 2017
q = sym([4 2 ; 2 4]);
f = sqrtm(q)^(-1) - sqrtm(q^(-1));
f should be zero here since q is positive definite.
However, the program yielded a non zero f here. Is this due to the calculation error ? Note that I am using symbolic calculation here so there should be no error at all I assume.

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John D'Errico
John D'Errico le 13 Fév 2017
Modifié(e) : John D'Errico le 13 Fév 2017
Sometimes the answer is just "simple".
simplify(f)
ans =
[ 0, 0]
[ 0, 0]
Symbolic results are not always returned in the most simple possible form.
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Qian Feng
Qian Feng le 13 Fév 2017
Thanks for the suggestion. I should have realized that.

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