Isn't the terminology here a little inconsistent? dims should probably be
called sizes.
Am Donnerstag, 19. Juni 2014 08:59:24 UTC+2 schrieb Ethan Anderes:
>
> I guess the docs are clear but for some reason I didn't understand it
> correctly after reading it a couple of times. Probably because I think of d
> as in Array{Float, d} rather than length. Should have looked more
> carefully. Sorry for the noise.
>
> d is the length of the transformed real array along the dims[1] dimension,
> which must satisfy d == floor(size(A,dims[1])/2)+1. (This parameter
> cannot be inferred fromsize(A) due to the possibility of rounding by the
> floor function here.)
>
>
>
> On Wednesday, June 18, 2014 11:54:33 PM UTC-7, Ethan Anderes wrote:
>>
>> That does it! I never would have guessed that dims would refer to the
>> side length of the matrix. Thanks a ton.
>>
>> On Wednesday, June 18, 2014 11:47:47 PM UTC-7, Alex wrote:
>>>
>>> Hi Ethan,
>>>
>>> irfft and brfft take an additional argument d, which roughly speaking
>>> denotes the size of the transformed matrix. See also the docs on brfft
>>> and irfft
>>> <http://julia.readthedocs.org/en/latest/stdlib/base/?highlight=brfft#Base.brfft>
>>>
>>> The following should work for you
>>> julia> a = rand(64, 64);
>>>
>>> julia> a_from_rfft = rfft(a);
>>>
>>> julia> back_to_a = irfft(a_from_rfft, size(a,1));
>>>
>>> julia> norm(back_to_a-a)
>>> 5.185263941656865e-15
>>>
>>> Hope that helps,
>>>
>>> Alex.
>>>
>>> On Thursday, 19 June 2014 06:37:38 UTC+2, Ethan Anderes wrote:
>>>>
>>>> Does anyone have experience with brfft or irfft? I’m trying to optimize
>>>> some code and I noticed a huge performance gain if I use rfft over fft for
>>>> 2-d real matrices. However
>>>> I need to filter in the Fourier domain, then use irfft (or brfft) to
>>>> return to spatial corridinates but I can’t seem to get irfft or brfft to
>>>> work.
>>>>
>>>> a = rand(1024, 1024);
>>>>
>>>> a_from_fft = fft(a);
>>>> a_from_rfft = rfft(a);
>>>>
>>>> ### each one of these gives an error
>>>> back_to_a = brfft(a_from_fft);
>>>> back_to_a = brfft(a_from_rfft);
>>>> back_to_a = irfft(a_from_fft);
>>>> back_to_a = irfft(a_from_rfft);
>>>>
>>>> Here is my version info
>>>>
>>>> julia> versioninfo()
>>>>
>>>> Julia Version 0.3.0-prerelease+3730
>>>> Commit 8f1fbec (2014-06-17 23:55 UTC)
>>>> Platform Info:
>>>> System: Darwin (x86_64-apple-darwin13.2.0)
>>>> CPU: Intel(R) Core(TM) i5-4250U CPU @ 1.30GHz
>>>> WORD_SIZE: 64
>>>> BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY)
>>>> LAPACK: libopenblas
>>>> LIBM: libopenlibm
>>>>
>>>>
>>>>
>>>
