GR4_EXTREMA - GR8_EXTREMA

GR4_EXTREMA(NXY,X,BVAL,EVAL,XMIN,XMAX,NMIN,NMAX)

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