# Solver Properties¶

The properties that characterize behaviors and supported features of SAPI solvers[1] can be queried through SAPI. This chapter defines these properties[2].

[1] | Ocean software also provides classical solvers such as dwave-greedy that you can run locally. See the Ocean documentation for information on parameters of such solvers. |

[2] | Ocean software classes such as the
`DWaveSampler` class may include various other
properties that are derived and stored client-side, not read from SAPI in the
`properties` dict; for example, the `dwave.cloud.solver.BaseSolver`
might derive an `avg_load` property. See the Ocean documentation for
those properties. |

The examples below use the following setup:

```
>>> from dwave.system import DWaveSampler, LeapHybridSampler
...
>>> qpu_advantage = DWaveSampler(solver={'topology__type': 'pegasus'})
>>> qpu_2000q = DWaveSampler(solver={'topology__type': 'chimera'})
>>> hybrid_bqm_sampler = LeapHybridSampler()
```

- anneal_offset_ranges
- anneal_offset_step
- anneal_offset_step_phi0
- annealing_time_range
- beta_range
- category
- chip_id
- couplers
- default_annealing_time
- default_beta
- default_programming_thermalization
- default_readout_thermalization
- extended_j_range
- h_gain_schedule_range
- h_range
- j_range
- max_anneal_schedule_points
- max_h_gain_schedule_points
- maximum_number_of_biases
- maximum_number_of_variables
- maximum_time_limit_hrs
- minimum_time_limit
- num_qubits
- num_reads_range
- parameters
- per_qubit_coupling_range
- problem_run_duration_range
- programming_thermalization_range
- quota_conversion_rate
- qubits
- readout_thermalization_range
- supported_problem_types
- tags
- topology
- version
- vfyc

## anneal_offset_ranges¶

Array of ranges of valid anneal offset values, in normalized offset units, for each qubit. The negative values represent the largest number of normalized offset units by which a qubit’s anneal path may be delayed. The positive values represent the largest number of normalized offset units by which a qubit’s anneal path may be advanced.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["anneal_offset_ranges"][50:55]
[[-0.6437569799443247, 0.5093937328282595],
[-0.6409899716199288, 0.5697835920492209],
[-0.6468663649068287, 0.5211452841036136],
[-0.6435316809914349, 0.5011584701861175],
[-0.6500326191157569, 0.5392206819650301]]
```

## anneal_offset_step¶

Quantization step size of anneal offset values in normalized units.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["anneal_offset_step"]
-0.00017565852000668507
```

## anneal_offset_step_phi0¶

Quantization step size in physical units (annealing flux-bias units): \(\Phi_0\).

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["anneal_offset_step_phi0"]
1.486239425109832e-05
```

## annealing_time_range¶

Range of time, in microseconds, possible for one anneal (read). The lower limit in this range is the fastest quench possible for this solver.

Default annealing time is specified by the default_annealing_time property.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["annealing_time_range"]
[1, 2000]
```

## category¶

Type of solver; for example,

`qpu`

—quantum computers such as the Advantage.`hybrid`

—quantum-classical hybrid; typically one or more classical algorithms run on the problem while outsourcing to a quantum processing unit (QPU) parts of the problem where it benefits most.`software`

—emulators such as a sampling emulator.

### Example¶

For the solver configured in the example setup above,

```
>>> hybrid_bqm_sampler.properties["category"]
'hybrid'
```

## chip_id¶

Name of the solver.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["chip_id"]
'Advantage_system1.1'
```

## couplers¶

Couplers in the working graph. A coupler contains two elements [*q1*, *q2*],
where both *q1* and *q2* appear in the list of working qubits, in the range
[0, *num_qubits* - 1] and in ascending order (i.e., *q1* < *q2*). These are the
couplers that can be programmed with nonzero \(J\) values.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["couplers"][:5]
[[30, 31], [31, 32], [32, 33], [33, 34], [34, 35]]
```

## default_annealing_time¶

Default time, in microseconds, for one anneal (read). You can change the annealing time for a given problem by using the annealing_time or anneal_schedule parameters, but do not exceed the upper limit given by the annealing_time_range property.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["default_annealing_time"]
20
```

## default_beta¶

Default value for \(\beta\).

## default_programming_thermalization¶

Default time, in microseconds, that the system waits after programming the QPU
for it to return to base temperature. This value contributes to the total
*qpu_programming_time*, which is returned by SAPI with the problem solutions.

You can change this value using the programming_thermalization parameter, but be aware that values lower than the default accelerate solving at the expense of solution quality.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["default_programming_thermalization"]
1000
```

## default_readout_thermalization¶

Default time, in microseconds, that the system waits after each state is read
from the QPU for it to cool back to base temperature. This value contributes to
the *qpu_delay_time_per_sample* field, which is returned by SAPI with the problem
solutions.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["default_readout_thermalization"]
0
```

## extended_j_range¶

Extended range of values possible for the coupling strengths (quadratic coefficients), \(J\), for this solver. Strong negative couplings may be necessary for some embeddings; however, such chains may require additional calibration through the flux_biases parameter to compensate for biases introduced by strong negative couplings. See also per_qubit_coupling_range.

extended \(J\) ranges and flux-bias offsets cannot be used with autoscaling (auto_scale) or spin-reversal transforms (num_spin_reversal_transforms).

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["extended_j_range"]
[-2.0, 1.0]
```

## h_gain_schedule_range¶

Range of the time-dependent gain applied to qubit biases for this solver.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["h_gain_schedule_range"]
[-4.0, 4.0]
```

## h_range¶

Range of values possible for the qubit biases (linear coefficients), \(h\), for this solver.

The auto_scale parameter, which rescales \(h\) and \(J\) values in the problem to use as much of the range of \(h\) (h_range) and the range of \(J\) (j_range) as possible, enables you to submit problems with values outside these ranges and have the system automatically scale them to fit.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["h_range"]
[-2.0, 2.0]
```

## j_range¶

Range of values possible for the coupling strengths (quadratic coefficients), \(J\), for this solver.

The auto_scale parameter, which rescales \(h\) and \(J\) values in the problem to use as much of the range of \(h\) (h_range) and the range of \(J\) (j_range) as possible, enables you to submit problems with values outside these ranges and have the system automatically scale them to fit.

See also extended_j_range.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["j_range"]
[-1.0, 1.0]
```

## max_anneal_schedule_points¶

Maximum number of points permitted in a PWL waveform submitted to change the default anneal schedule.

For reverse annealing, the maximum number of points allowed is one more than the number given in the max_anneal_schedule_points property.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["max_anneal_schedule_points"]
12
```

## max_h_gain_schedule_points¶

Maximum number of points permitted in a PWL waveform submitted to set a time-dependent gain on linear coefficients (qubit biases, see the h parameter) in the Hamiltonian.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["max_h_gain_schedule_points"]
20
```

## maximum_number_of_biases¶

Maximum number of biases, both linear and quadratic in total, accepted by the solver.

### Example¶

For the solver configured in the example setup above,

```
>>> hybrid_bqm_sampler.properties["maximum_number_of_biases"]
200000000
```

## maximum_number_of_variables¶

Maximum number of problem variables accepted by the solver.

### Example¶

For the solver configured in the example setup above,

```
>>> hybrid_bqm_sampler.properties["maximum_number_of_variables"]
1000000
```

## maximum_time_limit_hrs¶

Maximum allowed run time, in hours, that can be specified for the solver.

### Example¶

For the solver configured in the example setup above,

```
>>> hybrid_bqm_sampler.properties["maximum_time_limit_hrs"]
24.0
```

## minimum_time_limit¶

Minimum required run time, in seconds, the solver must be allowed to work on the given problem. Specifies the minimum time required for the given problem, as a piecewise-linear curve defined by a set of floating-point pairs. The second element is the minimum required time; the first element in each pair is some measure of the problem, dependent on the solver:

- For hybrid BQM solvers, this is the number of variables.
- For hybrid DQM solvers, this is a combination of the numbers of interactions, variables, and cases that reflects the “density” of connectivity between the problem’s variables.

The minimum time for any particular problem is a linear interpolation calculated
on two pairs that represent the relevant range for the given measure of the
problem. For example, if `minimum_time_limit`

for a hybrid BQM
solver were `[[1, 0.1], [100, 10.0], [1000, 20.0]]`

, then the minimum time
for a 50-variable problem would be 5 seconds, the linear interpolation of the
first two pairs that represent problems with between 1 to 100 variables.

For more details, see the Ocean samplers documentation for solver methods that calculate this parameter, and their descriptions.

### Example¶

For the solver configured in the example setup above,

```
>>> hybrid_bqm_sampler.properties["minimum_time_limit"]
[[1, 3.0],
[1024, 3.0],
[4096, 10.0],
[10000, 40.0],
[30000, 200.0],
[100000, 600.0],
[1000000, 600.0]]
```

## num_qubits¶

Total number of qubits, both working and nonworking, in the QPU.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["num_qubits"]
5760
```

## num_reads_range¶

Range of values possible for the number of reads that you can request for a problem.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["num_reads_range"]
[1, 10000]
```

## parameters¶

List of the parameters supported for the solver.

### Example¶

For the solver configured in the example setup above,

```
>>> hybrid_bqm_sampler.properties["parameters"]
{'time_limit': 'Maximum requested runtime in seconds.'}
```

## per_qubit_coupling_range¶

Coupling range permitted per qubit for this solver.

Strong negative couplings may be necessary for some embeddings, and can be enabled by using the extended_j_range range of \(J\) values. However, the total couplings for a qubit must not exceed the range specified by this property. Also, chains may require additional calibration through the flux_biases parameter to compensate for biases introduced by strong negative couplings.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["per_qubit_coupling_range"]
[-18.0, 15.0]
```

## problem_run_duration_range¶

Range of time, in microseconds, that a submitted problem is allowed to run.

The run-duration for a given problem, which is compared with this range, is calculated according to the following formula:

where \(P_1\), \(P_2\), \(P_3\), and \(P_4\) are the values specified for the annealing_time (or anneal_schedule), readout_thermalization, num_reads (samples), and programming_thermalization parameters, respectively.

Note

This is not the actual QPU access time of a given problem as that includes
programming time and readout time. For more information, see the *Solver Computation Time*
guide.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["problem_run_duration_range"]
[0, 1000000]
```

## programming_thermalization_range¶

Range of time, in microseconds, possible for the system to wait after programming
the QPU for it to cool back to base temperature. This value contributes to the
total *qpu_programming_time*, which is returned by SAPI with the problem
solutions.

You can change this value using the programming_thermalization parameter, but be aware that values lower than the default accelerate solving at the expense of solution quality.

Default value for a solver is given in the default_programming_thermalization property.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["programming_thermalization_range"]
[0, 10000]
```

## quota_conversion_rate¶

Rate at which user or project quota is consumed for the solver as a ratio to QPU solver usage. Different solver types may consume quota at different rates.

Time is deducted from your quota according to:

See the *Solver Computation Time* guide for more information.

### Example¶

For the solver configured in the example setup above,

```
>>> hybrid_bqm_sampler.properties["quota_conversion_rate"]
20
```

## qubits¶

Indices of the working qubits in the working graph.

Note

In a D-Wave QPU, the set of qubits and couplers that are available for
computation is known as the *working graph*. The yield of a working graph is
typically less than the total number of qubits and couplers that are
fabricated and physically present in the QPU.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["qubits"][:5]
[30, 31, 32, 33, 34]
```

## readout_thermalization_range¶

Range of time, in microseconds, possible for the system to wait after each state
is read from the QPU for it to cool back to base temperature. This value
contributes to the *qpu_delay_time_per_sample* field, which is returned by SAPI
with the problem solutions.

Default readout thermalization time is specified in the default_readout_thermalization property.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["readout_thermalization_range"]
[0, 10000]
```

## supported_problem_types¶

Indicates what problem types are supported for the solver.

QPU and QPU-like solvers support the following energy-minimization problem types:

`qubo`

—Quadratic unconstrained binary optimization (QUBO) problems; use \(0/1\)-valued variables.`ising`

—Ising model problems; use \(-1/1\)-valued variables.

Hybrid solvers support the following energy-minimization problem types:

`bqm`

—binary quadratic model (BQM) problems; use \(0/1\)-valued variables and \(-1/1\)-valued variables.`dqm`

—discrete quadratic model (DQM) problems; use variables that can represent a set of values such as`{red, green, blue, yellow}`

or`{3.2, 67}`

.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["supported_problem_types"]
['ising', 'qubo']
```

## tags¶

May hold attributes about a solver that you can use to have a client program choose one solver over another.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_2000q.properties["tags"]
['lower_noise']
```

## topology¶

Indicates the topology `type`

(`chimera`

or `pegasus`

) and `shape`

of
the QPU graph.

### Example¶

The topology seen in this example is a C16 Chimera graph, meaning that the D-Wave 2000Q QPU has 16 x 16 blocks of Chimera unit cells, and each unit cell has K4,4 connectivity.

For the solver configured in the example setup above,

```
>>> qpu_2000q.properties["topology"]
{'type': 'chimera', 'shape': [16, 16, 4]}
```

## version¶

Version number of the solver.

### Example¶

For the solver configured in the example setup above,

```
>>> hybrid_bqm_sampler.properties["version"]
'2.0'
```

## vfyc¶

Flag indicating whether this solver is a VFYC solver.

### Example¶

For the solver configured in the example setup above,

```
>>> qpu_advantage.properties["vfyc"]
False
```