Calculate more numerically accurate lower bound.

In roof duality, we convert a bqm to a posiform , convert its coefficients to integer coefficients, then convert it to an implication graph and find the max flow. We use the max flow to compute the lower bound of the bqm, but we may be able to take the original posiform use the fixed variables and find the lower bound. This will bypass the float-to-integer and integer-to-float conversions and provide a more accurate lower bound. We need to find out a way how to use the original posiform since roof duality will not fix all the variables in the posiform.

Comienza rastreando el flujo de roof duality desde el BQM a través de la posiform, las fixed variables, el implication graph y max flow. Determina cómo la posiform original podría producir el lower bound sin conversiones de float-to-integer e integer-to-float, incluidas las variables que roof duality no fija; se considera terminado cuando se obtiene un lower bound numéricamente más preciso.

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