As long as you're using the return value from qr(), qr is always allocating
the memory for "a" inside itself. You need to use qrfact!() to avoid some
allocation:
julia> A = randn(4,4)
4x4 Array{Float64,2}:
1.10997 1.27173 -0.997429 -0.916055
1.50834 0.691077 0.0358451 -0.200697
-0.522316 1.27148 1.32542 0.776502
0.622128 -0.567629 0.331535 0.829938
julia> qrfact!(A)
QRCompactWY{Float64}(4x4 Array{Float64,2}:
-2.04132 -0.703816 0.753963 0.592149
0.478643 1.88106 0.416794 -0.19707
-0.165747 -0.74871 -1.45624 -1.26801
0.19742 0.448426 0.166636 0.416953,4x4
Triangular{Float64,Array{Float64,2},:U,false}:
1.54375 -1.21153 -1.18989 0.0
0.0 1.1353 1.489 0.0
0.0 0.0 1.94597 0.0
0.0 0.0 0.0 0.0)
julia> A
4x4 Array{Float64,2}:
-2.04132 -0.703816 0.753963 0.592149
0.478643 1.88106 0.416794 -0.19707
-0.165747 -0.74871 -1.45624 -1.26801
0.19742 0.448426 0.166636 0.416953
So you can see that A has been clobbered, because we're reusing that memory.
-E
On Tue, Oct 7, 2014 at 4:04 PM, Ryan Young <[email protected]> wrote:
> Thanks for the reply.
>
> I think this still suffers from the same issue of allocating tmp every
> iteration through the loop. I only need to store the output of qr() if
> certain criteria are met. Then I do as you recommended and push it into a
> array. Consider the following
>
> function test_qr3(iters)
> tmp=rand(3,3)
> a=Array{Array{Float64,2},1}
> for i=1:iters
> a=qr(tmp)
> end
> end
>
> julia> @time test_qr3(100000)
> elapsed time: 0.474589094 seconds (147200224 bytes allocated)
>
> julia> @time test_qr3(200000)
> elapsed time: 0.90662408 seconds (294400224 bytes allocated)
>
>
> While this is a trivial example, there should be a way to make it so that
> 'a' is not re-alloacted each time through the loop. Or maybe the allocation
> is happening within qr()?
>
> Thanks
>
>
>
>
> On Tuesday, October 7, 2014 3:29:01 PM UTC-7, Max Suster wrote:
>>
>>
>> You could try this.
>>
>> a= Array{Float64,2}[]
>> b= Array{Float64,2}[]
>>
>> function test_qr(a,b)
>>
>> for i=1:100000
>> tmp = qr(rand(3,3))
>> push!(a,tmp[1])
>> push!(b,tmp[2])
>> end
>>
>> end
>>
>> julia> size(a,1)
>> 100000
>>
>> julia> size(b,1)
>> 100000
>>
>>
>> On Tuesday, October 7, 2014 10:17:07 PM UTC+2, Ryan Young wrote:
>>>
>>> Hello,
>>>
>>> I am working on optimizing a code that looks at 3D deformation fields.
>>> At one point I have to take the QR decompositions at many points. My
>>> problem is that regardless of how I pre-allocate my variables to store the
>>> results of the QR, they are allocated each time through the loop. I tried
>>> to use the qrfact! method but found it suffered from the same problem. Any
>>> help in getting around this would be great. A basic function that has the
>>> same problem is below.
>>>
>>> function test_qr()
>>> tmp=rand(3,3)
>>> a=Array(Float64,2)
>>> b=Array(Float64,2)
>>>
>>> for i=1:100000
>>> a,b=qr(tmp)
>>> end
>>>
>>> end
>>>
>>
