Covariant matrix as component type

[wdconinc]

Instead of covariant matrices stored as std::array<float,6> etc, we may want to use a component such as:

  eicd::Cov3f:
    Members:
      - float xx
      - float yy
      - float zz
      - float xy
      - float xz
      - float yz
    ExtraCode:
      declaration: "
        Cov3f() : xx{0}, yy{0}, zz{0}, xy{0}, xz{0}, yz{0} {}\n
        Cov3f(double vx, double vy, double vz, double vxy = 0, double vxz = 0, double vyz = 0)\n
          : xx{static_cast<float>(vx)}, yy{static_cast<float>(vy)}, zz{static_cast<float>(vz)},\n
            xy{static_cast<float>(vxy)}, xz{static_cast<float>(vxz)}, yz{static_cast<float>(vyz)} {}\n
        float operator()(unsigned i, unsigned j) const {\n
          // diagonal\n
          if (i == j) {\n
            return *(&xx + i);\n
          }\n
          // off-diagonal\n
          // we have as options (0, 1), (0, 2) and (1, 2) (and mirrored)\n
          // note that, starting from xy, we find the correct element at (i+j-1)\n
          return *(&xy + i + j - 1);\n
        }\n
      "

(Our extra utilities are in Vector3f.h, keeping them outside of the data model)

[tmadlener]

Fixed with #287