dwave-qbsolv 0.2.8

qbsolv
======

[](https://travis-ci.org/dwavesystems/qbsolv)
[](https://ci.appveyor.com/project/dwave-adtt/qbsolv/branch/master)

A decomposing solver, finds a minimum value of a large quadratic unconstrained binary optimization (QUBO) problem by
splitting it into pieces solved either via a D-Wave system or a classical tabu solver.

_(Note that qbsolv by default uses its internal classical solver. Access to a D-Wave system must be arranged separately.)_

Installation or Building
------------------------

#### Python

A wheel might be available for your system on pypi. Source distributions are provided as well.

```bash
pip install dwave-qbsolv
```

Alternately, you can build the library with setuptools

```bash
pip install -r python/requirements.txt
pip install cython==0.27
python setup.py install
```

#### C
To build the C library use cmake to generate a build command for your system. On Linux the commands would be something
like this:

```
mkdir build; cd build
cmake ..
make
```

To build the command line interface turn the cmake option `QBSOLV_BUILD_CMD` on. The command line option for cmake to do
this would be `-DQBSOLV_BUILD_CMD=ON`. To build the tests turn the cmake option `QBSOLV_BUILD_TESTS` on. The command
line option for cmake to do this would be `-DQBSOLV_BUILD_TESTS=ON`.

Command Line Usage
------------------

```
qbsolv -i infile [-o outfile] [-m] [-T] [-n] [-S SubMatrix] [-w]
[-h] [-a algorithm] [-v verbosityLevel] [-V] [-q] [-t seconds]

DESCRIPTION
qbsolv executes a quadratic unconstrained binary optimization
(QUBO) problem represented in a file, providing bit-vector
result(s) that minimizes (or optionally, maximizes) the value of
the objective function represented by the QUBO. The problem is
represented in the QUBO(5) file format and notably is not limited
to the size or connectivity pattern of the D-Wave system on which
it will be executed.
The options are as follows:
-i infile
The name of the file in which the input QUBO resides. This
is a required option.
-o outfile
This optional argument denotes the name of the file to
which the output will be written. The default is the
standard output.
-a algorithm
This optional argument chooses nuances of the outer loop
algorithm. The default is o.
'o' for original qbsolv method. Submatrix based upon change in energy.
'p' for path relinking. Submatrix based upon differences of solutions
-m
This optional argument denotes to find the maximum instead
of the minimum.
-T target
This optional argument denotes to stop execution when the
target value of the objective function is found.
-t timeout
This optional argument stops execution when the elapsed
cpu time equals or exceeds timeout value. Timeout is only checked
after completion of the main loop. Other halt values
such as 'target' and 'repeats' will halt before 'timeout'.
The default value is 2592000.0.
-n repeats
This optional argument denotes, once a new optimal value is
found, to repeat the main loop of the algorithm this number
of times with no change in optimal value before stopping.
The default value is 50.
-S subproblemSize
This optional argument indicates the size of the sub-
problems into which the QUBO will be decomposed. A
"-S 0" or "-S" argument not present indicates to use the
size specified in the embedding file found in the workspace
set up by DW. If a DW environment has not been established,
the value will default to (47) and will use the tabu solver
for subproblem solutions. If a value is specified, qbsolv uses
that value to create subproblem and solve with the tabu solver.
-w
If present, this optional argument will print the QUBO
matrix and result in .csv format.
-h
If present, this optional argument will print the help or
usage message for qbsolv and exit without execution.
-v verbosityLevel
This optional argument denotes the verbosity of output. A
verbosityLevel of 0 (the default) will output the number of
bits in the solution, the solution, and the energy of the
solution. A verbosityLevel of 1 will output the same
information for multiple solutions, if found. A
verbosityLevel of 2 will also output more detailed
information at each step of the algorithm. This increases
the output up to a value of 4.
-V
If present, this optional argument will emit the version
number of the qbsolv program and exit without execution.
-q
If present, this optional argument triggers printing the
format of the QUBO file.
-r seed
Used to reset the seed for the random number generation

------------------------
qbsolv "qubo" input file format

A .qubo file contains data which describes an unconstrained
quadratic binary optimization problem. It is an ASCII file comprised
of four types of lines:

1) Comments - defined by a "c" in column 1. They may appear
anywhere in the file, and are otherwise ignored.

2) One program line, which starts with p in the first column.
The program line must be the first non-comment line in the file.
The program line has six required fields (separated by space(s)),
as in this example:

p qubo topology maxNodes nNodes nCouplers

where:
p the problem line sentinel
qubo identifies the file type
topology a string which identifies the topology of the problem
and the specific problem type. For an unconstrained problem,
target will be "0" or "unconstrained." Possible, for future
implementations, valid strings might include "chimera128"
or "chimera512" (among others).
maxNodes number of nodes in the topology.
nNodes number of nodes in the problem (nNodes <= maxNodes).
Each node has a unique number and must take a value in the
the range {0 - (maxNodes-1)}. A duplicate node number is an
error. The node numbers need not be in order, and they need
not be contiguous.
nCouplers number of couplers in the problem. Each coupler is a
unique connection between two different nodes. The maximum
number of couplers is (nNodes)^2. A duplicate coupler is
an error.

3) nNodes clauses. Each clause is made up of three numbers. The
numbers are separated by one or more blanks. The first two
numbers must be integers and are the number for this node
(repeated). The node number must be in {0 , (maxNodes-1)}.
The third value is the weight associated with the node, may be
an integer or float, and can take on any positive or negative
value, or zero.

4) nCouplers clauses. Each clause is made up of three numbers. The
numbers are separated by one or more blanks. The first two
numbers must be different integers and are the node numbers
for this coupler. The two values (i and j) must have (i < j).
Each number must be one of the nNodes valid node numbers (and
thus in {0, (maxNodes-1)}). The third value is the strength
associated with the coupler, may be an integer or float, and can
take on any positive or negative value, but not zero. Every node
must connect with at least one other node (thus must have at least
one coupler connected to it).

Here is a simple QUBO file example for an unconstrained QUBO with 4
nodes and 6 couplers. This example is provided to illustrate the
elements of a QUBO benchmark file, not to represent a real problem.

| <--- column 1
c
c This is a sample .qubo file
c with 4 nodes and 6 couplers
c
p qubo 0 4 4 6
c ------------------
0 0 3.4
1 1 4.5
2 2 2.1
3 3 -2.4
c ------------------
0 1 2.2
0 2 3.4
1 2 4.5
0 3 -2
1 3 4.5678
2 3 -3.22
```

Library usage
-------------

TODO

Contribution
------------

See `contrib.txt`