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### 9.6 Applying Permutations

— Function: int gsl_permute (const size_t * p, double * data, size_t stride, size_t n)

This function applies the permutation p to the array data of size n with stride stride.

— Function: int gsl_permute_inverse (const size_t * p, double * data, size_t stride, size_t n)

This function applies the inverse of the permutation p to the array data of size n with stride stride.

— Function: int gsl_permute_vector (const gsl_permutation * p, gsl_vector * v)

This function applies the permutation p to the elements of the vector v, considered as a row-vector acted on by a permutation matrix from the right, v' = v P. The j-th column of the permutation matrix P is given by the p_j-th column of the identity matrix. The permutation p and the vector v must have the same length.

— Function: int gsl_permute_vector_inverse (const gsl_permutation * p, gsl_vector * v)

This function applies the inverse of the permutation p to the elements of the vector v, considered as a row-vector acted on by an inverse permutation matrix from the right, v' = v P^T. Note that for permutation matrices the inverse is the same as the transpose. The j-th column of the permutation matrix P is given by the p_j-th column of the identity matrix. The permutation p and the vector v must have the same length.

— Function: int gsl_permutation_mul (gsl_permutation * p, const gsl_permutation * pa, const gsl_permutation * pb)

This function combines the two permutations pa and pb into a single permutation p, where p = pa * pb. The permutation p is equivalent to applying pb first and then pa.

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