struct xf::fintech::FdG2SwaptionEngine::NinePointLinear

the round up the basic operators using in mixed-derivative

// fields

DT a00[_layoutSizeMax]
DT a01[_layoutSizeMax]
DT a02[_layoutSizeMax]
DT a10[_layoutSizeMax]
DT a11[_layoutSizeMax]
DT a12[_layoutSizeMax]
DT a20[_layoutSizeMax]
DT a21[_layoutSizeMax]
DT a22[_layoutSizeMax]