### 7.12 Elementary Operations

The following functions allow for the propagation of errors when combining quantities by multiplication. The functions are declared in the header file `gsl_sf_elementary.h`.

Function: int gsl_sf_multiply_e (double x, double y, gsl_sf_result * result)

  This function multiplies x and y storing the product and its associated error in result.

Function: int gsl_sf_multiply_err_e (double x, double dx, double y, double dy, gsl_sf_result * result)

  This function multiplies x and y with associated absolute errors dx and dy. The product xy +/- xy \sqrt((dx/x)^2 +(dy/y)^2) is stored in result.