  Using GPGPU techniques and multi-precision calculation we developed the code
to study QCD phase transition line in the canonical approach. The canonical
approach is a powerful tool to investigate sign problem in Lattice QCD. The
central part of the canonical approach is the fugacity expansion of the grand
canonical partition functions. Canonical partition functions $Z_n(T)$ are
coefficients of this expansion. Using various methods we study properties of
$Z_n(T)$. At the last step we perform cubic spline for temperature dependence
of $Z_n(T)$ at fixed $n$ and compute baryon number susceptibility $\chi_B/T^2$
as function of temperature. After that we compute numerically $\partial\chi/
\partial T$ and restore crossover line in QCD phase diagram. We use improved
Wilson fermions and Iwasaki gauge action on the $16^3 \times 4$ lattice with
$m_{\pi}/m_{\rho} = 0.8$ as a sandbox to check the canonical approach. In this
framework we obtain coefficient in parametrization of crossover line
$T_c(\mu_B^2)=T_c\left(c-\kappa\, \mu_B^2/T_c^2\right)$ with $\kappa = -0.0453
\pm 0.0099$.
