Searching 2D histogram ranges

The following functions are used by the access and update routines to locate the bin which corresponds to a given @math{(x\,y)} coordinate.

Function: int gsl_histogram2d_find (const gsl_histogram2d * h, double x, double y, size_t * i, size_t * j)

This function finds and sets the indices i and j to the to the bin which covers the coordinates (x,y). The bin is located using a binary search. The search includes an optimization for histogram with uniform ranges, and will return the correct bin immediately in this case. If @math{(x,y)} is found then the function sets the indices (i,j) and returns GSL_SUCCESS. If @math{(x,y)} lies outside the valid range of the histogram then the function returns GSL_EDOM and the error handler is invoked.