[julia-users] gigantic memory allocation

[wgao1]

Hi Julia Users

I write a small function to do Gram-Schmidt orthogonalization:

function ModGS(A::Array{Float64,2})
      delta = 1e-16
      (m,n) = size(A)
      for j = 1: n
          q = A[:,j]
          q = q / (norm(q)+delta)
          A[:,j] = q
          for k = j+1: n
               a = A[:,k]
               r = dot(q, a)
               A[:,k] = a - r*q
          end
      end
      return nothing
end

A = rand(1000, 500);
@time ModGS(A);

0.696324 seconds (875.25 k allocations: 2.831 GB, 15.78% gc time)


it cause huge amount of memory allocation, Does anybody know the reason? How to 
improve it?


I also use memory track tool, this is the output:

        - function ModGS(A::Array{Float64, 2})

 65440991     delta = 1e-16

        0     (m,n) = size(A)

        0     for j = 1: n

  4056000         q = A[:,j]

  4040000         q = q / (norm(q)+delta)

        0         A[:,j] = q

        0         for k = j+1: n

1011972000            a = A[:,k]

        0             r = dot(q, a)

2019952000            A[:,k] = a - r*q

        -         end

        -     end

        0     return nothing

        - end

        - 

        - 

        - A = randn(1000, 500);

        - ModGS(A)

        - 


Thanks