Compute the extrema of the input array avoiding blanked values.
Arguments : NXY INTEGER Input Number of points X REAL (NXY) Input Array BVAL REAL Input Blanking value EVAL REAL Input Tolerance on blanking XMIN REAL Output Minimum value XMAX REAL Output Maximum value NMIN INTEGER Output Pixel of the minimum X(NMIN) = XMIN NMAX INTEGER Output Pixel of the maximum