### Vector operations

The following operations are only defined for real vectors.

Function: int gsl_vector_add (gsl_vector * a, const gsl_vector * b)
  This function adds the elements of vector b to the elements of vector a, a'_i = a_i + b_i. The two vectors must have the same length.

Function: int gsl_vector_sub (gsl_vector * a, const gsl_vector * b)
  This function subtracts the elements of vector b from the elements of vector a, a'_i = a_i - b_i. The two vectors must have the same length.

Function: int gsl_vector_mul (gsl_vector * a, const gsl_vector * b)
  This function multiplies the elements of vector a by the elements of vector b, a'_i = a_i * b_i. The two vectors must have the same length.

Function: int gsl_vector_div (gsl_vector * a, const gsl_vector * b)
  This function divides the elements of vector a by the elements of vector b, a'_i = a_i / b_i. The two vectors must have the same length.

Function: int gsl_vector_scale (gsl_vector * a, const double x)
  This function multiplies the elements of vector a by the constant factor x, a'_i = x a_i.

Function: int gsl_vector_add_constant (gsl_vector * a, const double x)
  This function adds the constant value x to the elements of the vector a, a'_i = a_i + x.