/*****************************************************************************
*                                                                            *
*   ISNAN.SPL   Copyright (C) 2002 DSP Development Corporation               *
*                               All Rights Reserved                          *
*                                                                            *
*   Author:      Randy Race                                                  *
*                                                                            *
*   Synopsis:    Returns 1 for each element that is NA                       *
*                                                                            *
*   Revisions:    9 Aug 2002  RRR  Creation                                  *
*                                                                            *
*****************************************************************************/


#if @HELP_ISNAN

    ISNAN

    Purpose: Returns 1 for each element that is a NA value

    Syntax:  ISNAN(ser)

              ser - Series

    Returns: A series where each element is 1 where the input series is
             an NA value and 0 where the input series is not an NA value.

    Example:
             a = {1, 2, nan, 3};
             b = 5;
             c = {};

             isnan(a) returns {0, 0, 1, 0}
             isnan(b) returns {0}
             isnan(c) returns {}

    Remarks:
             ISNAN always returns a series.

             ISNAN returns an empty series if the input is an empty series.

    See Also:
             Finite
             Isempty
             Isinf
#endif


/* where is input NA? */
isnan(a)
{
        if (argc < 1) error("isnan - input required");

        if (iswinempty(a))
        {
                a = {};
        }
        else if (not(isarray(a)))
        {
                /* convert to series if not already */
                a = castseries(a);
        }

        return(isnavalue(a));
}