## Reduce negative sign for a given model

[MKrbm]

Algorithm

• (simulation) Is there any advantage of similarity transformation over unitary transformation in terms of reducing negative elements in matrix?

• (simulation) develop algorithm for minimizing ground state energies for absolute matrix

• Implement reweighting method for reduce negative sign (turns out that it is meeningless)

• advantage of unitary matrix over orthogonal matrix

• Implement riemannian optimization

Frustration-free model

• (Theoretically) All frustration-free models can transform into the non-negative-sign models at zero temperature?

• (Theoretically) If absolute map of local hamiltonian has the same ground-state energies spectrum, then the model after absolute map is also a frustration-free model?

• (simulation) Apply algorithm

[MKrbm]

Now, implementing reweighting method.