Quick Reference: Solutions

The Sol class represents a solution to a QUBO problem. It stores variable assignments along with the energy value and time-to-solution.

Creating a Sol

Expression	Description
`Sol(expr)`	Create an all-zero solution for expression `expr`

Getting Variable Values

Expression	Return Type	Description
`sol(x)`	`int`	Evaluate `Var` `x` (returns 0 or 1)
`sol(t)`	`int`	Evaluate `Term` `t`
`sol(f)`	`int`	Evaluate `Expr` `f`

For arrays, use element-wise access:

for i in range(n):
    print(sol(x[i]))

Setting Variable Values

Expression	Description
`sol.set(x, value)`	Set variable `x` to `value` (0 or 1)
`sol.set(other_sol)`	Copy all variable values from another `Sol`
`sol.set([(x, val), ...])`	Set variable values from a list of pairs
`sol.set([other_sol, [(x, val), ...]])`	Copy from `Sol`, then apply pair list

sol.set([(x[0], 1), (x[1], 0), (vi, 5)])

The set method returns self, allowing chaining:

full_sol = Sol(f).set([sol, [(x[0], 1)]])

Energy and Evaluation

Expression	Return Type	Description
`sol.energy`	`int`	Return the stored energy value
`sol.comp_energy()`	`int`	Recompute energy from current variable values and store it
`sol.tts`	`float`	Time-to-solution (seconds)

sol.energy is a property that returns the energy value stored when the solver found the solution. It does not recompute the energy. After calling sol.set() to modify variable values, the stored energy becomes invalid. Accessing sol.energy in this state raises an error. Call sol.comp_energy() to recompute and update the energy before accessing it.

Extracting Integers from Solutions

`onehot_to_int()` — One-Hot Decoding

Expression	Return Type	Description
`qbpp.onehot_to_int(sol(x))`	`Array`	Decode one-hot along last axis (default)
`qbpp.onehot_to_int(sol(x), k)`	`Array`	Decode one-hot along axis $k$

Decodes along the specified axis and returns an array with one fewer dimension. The output shape is the input shape with axis $k$ removed, and each element is the index of the 1 along that axis. Negative indices are supported (e.g., -1 = last axis). Returns $-1$ for slices that are not valid one-hot vectors.

For more details and examples, see One-Hot to Integer Conversion.

Solver Info

The solver result classes (EasySolverSol, ExhaustiveSolverSol, ABS3SolverSol) inherit from Sol and provide additional information via info.

Expression	Return Type	Description
`sol.info`	`dict`	Key-value pairs of solver information
`sol.sols()`	`list[Sol]`	All collected solutions
`sol.size()`	`int`	Number of collected solutions
`sol[i]`	`Sol`	Access the $i$-th solution

The info dictionary contains solver metadata as string key-value pairs. Representative keys include:

Key	Description
`"flip_count"`	Total number of variable flips performed
`"var_count"`	Number of variables in the model
`"term_count"`	Number of terms in the model
`"version"`	QUBO++ version
`"cpu_name"`	CPU model name
`"hostname"`	Machine hostname

for k, v in sol.info.items():
    print(f"{k} = {v}")

Printing

print(sol)