/***********************************************************************************
    Copyright 2011 Bryan Johnson, Xiaoyue Guan & Charles F. Gammie

                  mthreed  version 1.0   (released Jun 2, 2011)

    This file is part of mthreed. mthreed adopts a ZEUS-like scheme to solve 
    magnetohydrodynamic equations of motion in a shearing sheet. It uses obital 
    advection to ensure fast and accurate integration in a large shearing box. 
    

    You are morally obligated to cite the following paper in his/her
    scientific literature that results from use of any part of mthreed:

    [1] Johnson, B.M., Guan, X. \& Gammie, C.F. \ 2008, Astrophysical Journal, 
        Supplement, 177, 373


    The latest version of the mthreed is available on our code distribution
    website:
    http://rainman.astro.uiuc.edu/codelib/

    mthreed is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    mthreed is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with mthreed; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

***********************************************************************************/

this is for mthreed paper version,

THE BASIC algorithm is as follows:
---------------------
1. all the sequence of the code is as the orginal mthreed
2. the way the flux is calculated is changed, which involves 
    a. the momentum flux -> step_trans_new.c
    b. the flux adv in BCs -> remap.c
3. we use a faster timestep.
4. we eliminate redundant arrays here, so it uses less memory.