/*****************************************************************************
*                                                                            *
*   TRIU.SPL     Copyright (C) 2002 DSP Development Corporation              *
*                               All Rights Reserved                          *
*                                                                            *
*   Author:      Randy Race                                                  *
*                                                                            *
*   Synopsis:    Returns upper triangle                                      *
*                                                                            *
*   Revisions:   13 Aug 2002  RRR  Creation                                  *
*                                                                            *
*****************************************************************************/

#include 

#if @HELP_TRIU

    TRIU

    Purpose: Returns the upper triangle of a matrix

    Syntax:  TRIU(m, d)

                  m -  An array.

                  d -  Optional An integer, the diagonal on and below which
                       to include matrix elements. Defaults to 0, the main
                       diagonal.


    Returns: An array consisting of the upper triangle of m where the other
             elements are zero.

    Example:
             W1: {{1, 2, 3},
                  {4, 5, 6},
                  {7, 8, 9}}

             W2: triu(w1)

             W2 == {{1, 2, 3},
                    {0, 5, 6},
                    {0, 0, 9}}


             W3: triu(W1, 1)

             W3 == {{0, 2, 3},
                    {0, 0, 6},
                    {0, 0, 0}}


             W4: triu(W1, -1)

             W4 == {{1, 2, 3},
                    {4, 5, 6},
                    {0, 8, 9}}


    Remarks:
             TRIU(m, 1) is equivalent to UPTRIX(m).

    See Also:
             TRIL
             UPLOTRI
             UPLOTRIX
#endif



/* upper triangle */
triu(M, d)
{
        if (argc < 2)
        {
                if (argc < 1) error("triu - input array required");
                
                d = 0;
        }
        
        if (not(isarray(M))) M = castseries(M);

        return((M)*(rownos(M) <= (colnos(M) - d)));
}