* +-======-+ 
*  Copyright (c) 2003-2007 United States Government as represented by 
*  the Admistrator of the National Aeronautics and Space Administration.  
*  All Rights Reserved.
*  
*  THIS OPEN  SOURCE  AGREEMENT  ("AGREEMENT") DEFINES  THE  RIGHTS  OF USE,
*  REPRODUCTION,  DISTRIBUTION,  MODIFICATION AND REDISTRIBUTION OF CERTAIN 
*  COMPUTER SOFTWARE ORIGINALLY RELEASED BY THE UNITED STATES GOVERNMENT AS 
*  REPRESENTED BY THE GOVERNMENT AGENCY LISTED BELOW ("GOVERNMENT AGENCY").  
*  THE UNITED STATES GOVERNMENT, AS REPRESENTED BY GOVERNMENT AGENCY, IS AN 
*  INTENDED  THIRD-PARTY  BENEFICIARY  OF  ALL  SUBSEQUENT DISTRIBUTIONS OR 
*  REDISTRIBUTIONS  OF THE  SUBJECT  SOFTWARE.  ANYONE WHO USES, REPRODUCES, 
*  DISTRIBUTES, MODIFIES  OR REDISTRIBUTES THE SUBJECT SOFTWARE, AS DEFINED 
*  HEREIN, OR ANY PART THEREOF,  IS,  BY THAT ACTION, ACCEPTING IN FULL THE 
*  RESPONSIBILITIES AND OBLIGATIONS CONTAINED IN THIS AGREEMENT.
*  
*  Government Agency: National Aeronautics and Space Administration
*  Government Agency Original Software Designation: GSC-15354-1
*  Government Agency Original Software Title:  GEOS-5 GCM Modeling Software
*  User Registration Requested.  Please Visit http://opensource.gsfc.nasa.gov
*  Government Agency Point of Contact for Original Software:  
*  			Dale Hithon, SRA Assistant, (301) 286-2691
*  
* +-======-+ 
***************************************************************************************
*	$Id$
*	Copyright (C) 2004 Bin Guan.
*	Distributed under GNU/GPL.
***************************************************************************************
function astudt(arg)
*
* Calculate t for given dof and p in a two-tailed Student t-test. 
*
rc = gsfallow("on")
dof=subwrd(arg,1)
p=subwrd(arg,2)
tname=subwrd(arg,3)
if(p='')
usage()
return
endif
if(tname='')
tname='astudtout'
endif

v=0.5
dv=0.5
t=0

while(dv>1e-6)
t=1/v-1
dv=dv/2
'studt 'dof' 't
'q defval studtout 1 1'
*'q defval studtp 1 1'
studtp=subwrd(result,3)
if(studtp>p)
v=v-dv
else
v=v+dv
endif
endwhile

tname'='t
return
***************************************************************************************
function usage()
*
* Print usage information.
*
say '  Two-tailed Student t-test.'
say ''
say '  Usage: astudt <dof> <p> [<t>]'
say '     <dof>: degree of freedom.'
say '     <p>: probability.'
say '     <t>: t-statistic. Defaults to astudtout.'
say ''
say '  Dependencies: studt.gs'
say ''
say '  Copyright (C) 2004 Bin Guan.'
say '  Distributed under GNU/GPL.'
return