  A method is developed to compute minimal energy vortex lattices in a general
Ginzburg-Landau model of a superconductor subjected to an applied magnetic
field. The model may have any number of components and may be spatially
anisotropic. Both the period vectors of the vortex lattice, and the orientation
of its vortex lines, are determined dynamically; no assumptions are made about
them. Methods to compute the first and second critical magnetic fields,
$H_{c_1}$ and $H_{c_2}$, in this class of models are also developed.
  These methods are applied to a simple anisotropic single-component model, and
to an anisotropic two-component model of strong current theoretical interest (a
so-called $s+id$ model). It is found, in both cases, that at low applied field
the vortex lines can tilt very significantly away from the direction of the
applied field (by as much as $40^o$ for the single-component and $30^o$ for the
$s+id$ model). The optimal lattice in the $s+id$ model is qualitatively very
different from the conventional triangular Abrikosov lattice, exhibiting a
phase transition from a system of Skyrmion chains when the external field is
orthogonal to the basal plane to a deformed Abrikosov lattice when applied in
the basal plane.
