# How to speed the function H in this code? (Hausdorff Chirality Measurement)

Luis_Manuel_Espinoza

1m

I am trying to do the Hausdorff Chirality Measurement from the article by Andrzej B. Buda and Kurt Mislow* but as I thought it is taking too long because to obtain a reliable value, I need to take “n” greater than 1,000,000 and it is with structures of 35 atoms It takes me almost 20 minutes, I was thinking about how to speed it up but I haven’t been able to make progress, I don’t know if anyone has an idea to speed it up, I would try to do it with parallel computing but I have no experience.

``````function Compute_of_CM_R_CCM(coords)
# Compute the center of mass of the atoms
n = size(coords, 1)
center_of_mass = sum(coords, dims=1) / n
# Compute the distances between the center of mass and each atom
distances = zeros(n)
for i in 1:n
distances[i] = norm((center_of_mass.-coords)[i,:])
end
# Compute the radius of the smallest circle that encloses the atoms
#Compute the coordinates translated to the center of mass
coordinates_origin = coords .- center_of_mass

end

function ρ(Q,Qp)
n = size(Q,1)
sup = []
for i in 1:n
inf = []
for j in 1:n
dis = norm(Q[i,:].-Qp[j,:])
push!(inf,dis)
end
push!(sup,minimum(inf))
end
return maximum(sup)
end

D = []
for i in 1:n
distan = []
for j in i+1:n
push!(D,d)
end
end
return maximum(D)
end

function H(q,qp,n)
A = Compute_of_CM_R_CCM(q)[3]
B = Compute_of_CM_R_CCM(qp)[3]
HH = []
for i in 1:n
BB = B*qr(randn(3, 3)).Q
HCM = max(ρ(A,BB),ρ(BB,A))/dQ(A)
push!(HH,HCM)
end
return minimum(HH)
end

``````

Sorry, I forgot to add an example of coordinates that are being used:

``````s = [ 1.73761 -2.3299 4.09897
1.7145 -1.88395 2.6064
0.810808 -3.53329 4.43137
1.35042 -1.47855 4.72023
2.18376 -2.67875 1.98346
2.32905 -0.962011 2.49604
3.08037 -3.63788 4.84995
3.53686 -2.0441 5.09464
-0.656357 -2.61487 3.56265
3.11152 -2.69374 4.42536
1.24236 -4.55928 4.94814
2.0e-6 -1.53167 1.96559
-0.51205 -3.38046 4.19649]
``````

There are many inefficiencies in your code, but I’ll point out two important ones:

Firstly,

Make sure to never initialize vectors like this. These create a `Vector{Any}`, which means that the compiler has no way of knowing what kind of values are contained therein, and therefore cannot create fast specialized instructions.

Secondly,

Here (and other places, too) you painstakingly build a vector, but in the end you throw it away, just keeping the maximum. Instead just keep the running max:

``````function dQ(coordenadas)
dmax = 0.0
for i in 1:n
for j in i+1:n
dmax = max(dmax, d)
end
end
return dmax
end
``````

Always make sure to not create arrays if you don’t need them.

There’s a lot of other things as well, but those two struck me particularly.

BTW, if you want help to really speed this up, please provide example input data, so that posters can run the code themselves. Right now it’s not easy to guess what sort of input data should be used.

I’m sorry, I didn’t think it through

Can you show how you call `H`? It takes three different input arguments, how does `s` relate to those?

Ahhh the second argument could be ss =-1*s and n is an Int that helps us increase the precision of the method, the function H is defined below the other functions above.

But thank you very much, the two observations you made previously have made me see those errors.