## Xfoil: Multiple inviscid airfoil comparison to analytic solution

For a multi-element airfoil system, the procedure is identical to a single body system, except we input a vector of matrices for the coordinates of the various bodies.
For this case, we'll use data that comes from ["An Exact Test Case for the Plane Potential Flow About Two Adjacent Lifting Aerofoils" by B. R. Williams.](https://reports.aerade.cranfield.ac.uk/handle/1826.2/2993)

```@example Xfoil
using FLOWFoil

af_geom_path = normpath(joinpath(splitdir(pathof(FLOWFoil))[1], "..", "docs", "src", "assets", "two_inviscid_airfoils.jl"))
include(af_geom_path)

outputs = analyze(([ximain etamain], [xiflap etaflap]), 0.0; method=Xfoil())

# plot and save comparisons, hiding code #hide
# First panel: Airfoil geometry #hide
include("../assets/plots_default.jl") #hide
plt1 = plot( # hide
    ximain, etamain; # hide
    linecolor = 1, # hide
    linewidth = 2, # hide
    label = "Main Airfoil", # hide
    aspect_ratio = 1, # hide
    legend = :top, # hide
    framestyle = :none, # hide
    ticks = false, # hide
) # hide

plot!( # hide
    plt1, # hide
    xiflap, etaflap; # hide
    linecolor = 2, # hide
    linewidth = 2, # hide
    label = "Flap Airfoil" # hide
) # hide

# Second panel: Cp comparison #hide
scatter( # hide
    ximain, cpmain; # hide
    label = "Main Airfoil Analytic", # hide
    xlabel = L"x", # hide
    ylabel = L"c_p", # hide
    yflip = true, # hide
    legend = :topright, # hide
    color=1, # hide
    markerstrokewidth=0, # hide
    markersize=4, #hide
) # hide
scatter!( # hide
    xiflap, cpflap; # hide
    label = "Flap Analytic", # hide
    color = 2, # hide
    markerstrokewidth=0, # hide
    markersize=4, #hide
    ) # hide

plot!( # hide
    ximain[1:end-1], outputs.cp[1][:]; # hide
    label = "Main FLOWFoil", # hide
    color=2, #hide
    ylim=(-10,10), #hide
) # hide
plot!( # hide
    xiflap[1:end-1], outputs.cp[2][:]; # hide
    label = "Flap FLOWFoil", # hide
    color = 1, # hide
) # hide
```

We see excellent agreement with the analytical solution.


