Gaussian-Product Subdivision Surfaces

from linearalgebra: vec

icf_i = vec(c_i⁻¹)
qq1_i = (icf_i,1 , icf_i,2 , icf_i,3)
qq2_i = (icf_i,5 , icf_i,6 , icf_i,9)
qlin_i = c_i⁻¹ v_i,*

`v_out`_i = [qq1_iᵀ
             (qq1_i,2 , qq2_i,1 , qq2_i,2)ᵀ
             (qq1_i,3 , qq2_i,2 , qq2_i,3)ᵀ
             ]⁻¹ qlin_i

where

v ∈ ℝ^(m×3)
f ∈ ℤ^(t×3)
c_i ∈ ℝ^(3×3)
n ∈ ℤ