%% File README
 	
Licensing
The full software license for DMRG++ version 2.0.0 
can be found in
file LICENSE in the root directory of the code.
DMRG++ is a free and open source implementation of the 
DMRG algorithm. You are welcome to use it and publish data 
obtained with DMRG++. If you do, please cite this
work (see next subsection).

How To Cite This Work

@article{re:alvarez09,
author="G. Alvarez",
title="The density matrix renormalization group for strongly correlated electron
systems: A generic implementation",
journal="Computer Physics Communications",
volume="180",
pages="1572",
year="2009"}

And also:

@article{
re:webDmrgPlusPlus,
Author = {G. Alvarez},
Title = {DMRG++ Website},
Publisher = {\url{https://www.ornl.gov/~gz1/dmrgPlusPlus}} }

What's new in Version 2

* Engine: SU(2) symmetry now supported and integrated
* Engine: Checkpointing
* Engine: DiskStack to support checkpointing
* Engine: Faster WaveFunctionTransformation for local symmetries
* User Interface: Customizable finite sweeps
* New Model: FeBasedSc for Fe-based Superconductors
* New Geometry: GeometryLadderFeAs to go with FeBasedSc
* Tests: TestSuite added (under /TestSuite)
* Documentation: Manual added (under /doc)

Building and Running DMRG++
Required Software

* (required) GNU C++
* (required) The LAPACK library.
This library is available for most platforms.
The configure.pl script will ask for the LDFLAGS variable 
to pass to the compiler/linker. If the linux platform was
chosen the default/suggested LDFLAGS will include -llapack.
If the osx platform was chosen the default/suggested LDFLAGS will
include  -framework Accelerate.
For other platforms the appropriate linker flags must be given.
More information on LAPACK is here: https://netlib.org/lapack/
* (optional) make or gmake (only needed to use the Makefile)
* (optional) perl (only needed to run the configure.pl script)

Quick Start
To Build DMRG++:

cd src
perl configure.pl
(please answer questions regarding model, etc)
make

To Run DMRG++:

./dmrg input.inp

The files created by \cppFile{configure.pl} are the following:

\cppFile{main.cpp}: 
\cppFile{configure.pl} will create the file \cppFile{main.cpp}
which contains the entry point (function int main()) for DMRG++,
according to the answers to questions given.

\cppFile{Makefile}:
\cppFile{configure.pl} will create the file \cppFile{Makefile}
according to the answers to questions given. 
In the Makefile, LDFLAGS must contain the linker flags to 
link with the LAPACK library. Defaults provided 
 automatically by configure.pl should work in most cases.
If MPI is not selected (serial code) then the compiler will be chosen to be g++.
Other compilers may work but only the GNU C++ compiler, g++, was tested.
If MPI is selected then the compiler will be chosen to be mpicxx, which 
is usually a wrapper script around g++ to take care of linking with MPI libraries 
and to include MPI headers. Depending on your MPI installation you might need to
change the name of this script.

\cppFile{input.inp}:
\cppFile{configure.pl} will create the file \cppFile{input.inp}
according to the answers to questions given.
This file can be used as input to run the DMRG++ program, in the following way:
for serial code:

./dmrg input.inp

for MPI code: (actual command will vary according to MPI Installation):

mpirun ./dmrg input.inp

The Input File
There is a single input file that is passed as the first
and only argument to the program.
There are two kinds of parameters in the input file:
(i) model parameters, and (ii) DMRG Solver parameters.
The Model parameters vary from model to model.
The DMRG Solver parameters are discussed below.

\inputItem{Options}
A comma-separated list of strings. At least one of the following strings must be provided:
\inputSubItem{none}  Use this when no options are given, since the list of strings must be non-null.
Note that ``none'' does not disable other options.\\
\inputSubItem{hasQuantumNumbers} If this option is given, the program will read the line ``QNS'' 
described below and act accordingly. It is recommended that you set this option.  \\
\inputSubItem{wft}  Use the Wave Function Transformation speed-up, which is disabled by default.\\
\inputSubItem{useSu2Symmetry} Use the SU(2) symmetry for the model, and interpret quantum numbers in 
the line ``QNS'' appropriately. The option ``hasQuantumNumbers'' must be set for this to work.\\
\inputSubItem{nofiniteloops}  Don't do finite loops, even if provided under ``FiniteLoops'' below.\\
\inputItem{version}  A mandatory string that is read and ignored. Usually contains the result
of doing ``git rev-parse HEAD''.\\
\inputItem{outputfile}  The output file. This file will be created if non-existent, and if it
exits it will be truncated.\\
\inputItem{InfiniteLoopKeptStates}  ``m'' value for the infinite algorithm.\\
\inputItem{FiniteLoops} A series of space-separated numbers. More than one space is allowed.
The first number is the number of finite algorithm ``movements'', followed by series
of three numbers for each ``movement''. Of the three numbers, the first
is the number of sites to go forward if positive or backward if negative.
The second number is the ``m'' for this ``movement' and the last number is either 0 or 1,
0 will not save state data to disk and 1 will save all data to be able to calculate observables.
The first ``movement'' starts from where the infinite loop left off, at the middle of the lattice.\\
\inputItem{QNS}  A space-separated list of numbers. More than one space is allowed.
The first number is the number of numbers to follow, these numbers being the density of quantum
numbers for each conserved quantum number to be used.
In a simpler way, usually this is 3 followed by $n_\uparrow n_\downarrow 0$  if not using
SU(2) symmetry, where  $n_\uparrow$, and $n_\downarrow$ are the densities of up and down
electrons respectively. If there is SU(2) symmetry then this is 3 followed by $n_\uparrow n_\downarrow j$,
where $n_\uparrow$, and $n_\downarrow$ are the densities of up and down
electrons respectively, and $j$ is twice the angular momentum divided by the number of sites.

%% Extracted from the DMRG++ Manual
%% by ../scripts/extractFromManual.pl for README