Requirements:
*DiFX-2.4 or above
*GSL
*GSLCBLAS
*automake autoconf libtool

Description:

Limitations:
1. 2-bits sampling
2. Only generate single-thread multi-channel VDIF
3. Default SEFD for 3 antennas
4. VDIF packet of all antennas need to repsent the same time length

Installation:

 libtoolize --force
 aclocal -I m4
 autoheader
 automake --force-missing --add-missing
 autoconf
 ./configure --prefix=$HOME
 make
 make install


Usage:
1. source DiFX setup.bash file
2. source HOPS hops.bash file
3. 'datasim --help' shows a list of possible options 
4. generate v2d and VEX file: './genv2dvex.sh expDir datasim.inp',
   see for example datasim.inp.template for example settings
5. in the directory of the generated v2d and VEX file, 
   proceed to generate DiFX .input and .calc-->.im files
   'cd expDir-7000'
   'vex2difx expDir.7000.v2d'
   'calcif2 expDir_7000.calc'
6. in the same directory proceed to create simulated .vdif data:
   'datasim -f 100 -s 1000,2000,3000 -d 12345 expDir_7004.input'
    where -f is the source flux density, -s is a list of antenna SEFDs,
   -d is the random number seed