generate_ode_iW -> generate_factorized_W

[YingboMa]

The generated factorized W matrix is in the bare factors form. So, one can use it by

julia> factors = zeros(3, 3); F = LU(factors, collect(axes(factors, 1)), 0);

julia> fw(factors, u, p, 1, 1); F
LU{Float64,Array{Float64,2}}
L factor:
3×3 Array{Float64,2}:
  1.0   0.0  0.0
 -0.4   1.0  0.0
 -0.4  -6.5  1.0
U factor:
3×3 Array{Float64,2}:
 5.0  -4.0   0.0
 0.0   0.4   1.0
 0.0   0.0  13.5

[codecov]

Codecov Report

Merging #118 into master will decrease coverage by 0.33%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #118      +/-   ##
==========================================
- Coverage   94.52%   94.18%   -0.34%     
==========================================
  Files          11       11              
  Lines         329      327       -2     
==========================================
- Hits          311      308       -3     
- Misses         18       19       +1

Impacted Files	Coverage Δ
src/systems/diffeqs/diffeqsystem.jl	94% <100%> (-0.24%)	⬇️
src/operations.jl	85.71% <0%> (-7.15%)	⬇️

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