double precision function kutl_mass3(w1, w2, w3)
*
* begin_doc
*
*  Find the invariant mass of w1, w2 and w3. No position information is
*  used. If mass^2 < 0, then a negative value is returned.
*
*  Input Parameters:
*  w1(10)       double precision array
*               Input w track 1
*
*  w2(10)       double precision array
*               Input w track 2
*
*  w3(10)       double precision array
*               Input w track 3
*
*  Output Parameters:
*
*  Return value: Invariant mass of w1, w2
*
*  Other routines:
*
*  Notes:
*
*  Author:   Paul R Avery      Created:  Mon Jul 28 05:32:22 EDT 1997
*
*  Major revisions:
*
*
* end_doc