  We evaluate validity of NLFFF extrapolation performed with Optimization class
(OPTI) codes. While explaining inevitable for OPTI partial non-solenoidality
caused by the gas pressure notable role in pressure balance at photospheric
heights and by mathematical aspects related to optimization and BVP (boundary
value problem), we justify elimination of the non-solenoidal component
(postprocessing) from the OPTI result obtained. In essence, postprocessing
converts the entire non-solenoidal part into a solenoidal force part, which
possibly reflects factual deviation of magnetic field from its force-free
pproximation on the photosphere and in the solar corona. Two forms of
postprocessing have been analyzed in this paper.Postprocessing I eliminates the
non-solenoidal component without changing transverse field at the measurement
level, and Postprocessing II leaves the field normal component unchanged.
Extrapolation, postprocessing, and then comparison of metric and energy
characteristics are performed over AR 11158 active region for a small fragment
of its evolution containing the February X-class flare.Our version of OPTI code
showed that free energy decreased by $\sim 10^{32}$ erg within 1 hour, which
corresponds to theoretical estimations of the flare-caused magnetic energy
loss. This result differs significantly from the one in Sun et al.
(2012).Therefore, we also comment on some features of our OPTI code
implementation, which may cause significant differences between our results and
those obtained using the Wiegelmann (2004) version of OPTI code in study by Sun
et al. (2012).
