
plshades: Shade regions on the basis of value 

DESCRIPTION:

    This function is used in examples 16,21. 

SYNOPSIS:

plshades(a, nx, ny, defined, xmin, xmax, ymin, ymax, clevel, nlevel, fill_width, cont_color, cont_width, fill, rectangular, pltr, pltr_data)

ARGUMENTS:

    a (const PLFLT * const *, input) :      Contains ** pointer to array to
    be plotted. The array must have been declared as PLFLT a[nx][ny]. 

    nx (PLINT, input) :    First dimension of array "a". 

    ny (PLINT, input) :    Second dimension of array "a". 

    defined (PLINT (*) (PLFLT, PLFLT), input) :    User function
    specifying regions excluded from the shading plot.  This function
    accepts x and y coordinates as input arguments and must return 0
    if the point is in the excluded region or 1 otherwise. This
    argument can be NULL if all the values are valid. 

    xmin (PLFLT, input) :    Defines the "grid" coordinates.  The data
    a[0][0] has a position of (xmin,ymin), a[nx-1][0] has a position
    at (xmax,ymin) and so on. 

    xmax (PLFLT, input) :    Defines the "grid" coordinates.  The data
    a[0][0] has a position of (xmin,ymin), a[nx-1][0] has a position
    at (xmax,ymin) and so on. 

    ymin (PLFLT, input) :    Defines the "grid" coordinates.  The data
    a[0][0] has a position of (xmin,ymin), a[nx-1][0] has a position
    at (xmax,ymin) and so on. 

    ymax (PLFLT, input) :    Defines the "grid" coordinates.  The data
    a[0][0] has a position of (xmin,ymin), a[nx-1][0] has a position
    at (xmax,ymin) and so on. 

    clevel (const PLFLT *, input) :    Pointer to array containing the
    data levels corresponding to the edges of each shaded region that
    will be plotted by this function.  To work properly the levels
    should be monotonic. 

    nlevel (PLINT, input) :    Number of shades plus 1 (i.e., the number
    of shade edge values in clevel). 

    fill_width (PLFLT, input) :    Defines line width used by the fill
    pattern. 

    cont_color (PLINT, input) :    Defines pen color used for contours
    defining edges of shaded regions.  The pen color is only temporary
    set for the contour drawing.  Set this value to zero or less if no
    shade edge contours are wanted. 

    cont_width (PLFLT, input) :    Defines line width used for contours
    defining edges of shaded regions.  This value may not be honored
    by all drivers. The pen width is only temporary set for the
    contour drawing.  Set this value to zero or less if no shade edge
    contours are wanted. 

    fill (void (*) (PLINT, const PLFLT *, const PLFLT *), input) :   
    Routine used to fill the region.  Use plfill.  Future version of
    PLplot may have other fill routines. 

    rectangular (PLBOOL, input) :    Set rectangular to true if rectangles
    map to rectangles after coordinate transformation with pltrl. 
    Otherwise, set rectangular to false. If rectangular is set to
    true, plshade tries to save time by filling large rectangles. 
    This optimization fails if the coordinate transformation distorts
    the shape of rectangles. For example a plot in polar coordinates
    has to have  rectangular set to false. 

    pltr (void (*) (PLFLT, PLFLT, PLFLT *, PLFLT *, PLPointer) , input) : 
      Pointer to function that defines transformation between indices
    in array z and the world coordinates (C only).    Transformation
    functions are provided in the PLplot library: pltr0 for identity
    mapping, and pltr1 and pltr2 for arbitrary mappings respectively
    defined by one- and two-dimensional arrays.  In addition,
    user-supplied routines for the transformation can be used as well.
     Examples of all of these approaches are given in the PLplot
    documentation. The transformation function should have the form
    given by any of pltr0, pltr1, or pltr2. 

    pltr_data (PLPointer, input) :    Extra parameter to help pass
    information to pltr0, pltr1, pltr2, or whatever routine that is
    externally supplied. 
