Re: [Boost-users] C++ Performance

From: Mike Marchywka (marchywka_at_[hidden])
Date: 2007-12-04 07:42:07

> have to find the differences between them. Ideally, you should not see
> any difference. If you do notice a difference, check if the difference
> is negligible (you have to decide the precision you are expecting).

Normally with numerical stuff, diff wouldn't be easy unless you knock down precision
but, even then you may often want to at least look at the noise. I think this wavelet
transform is invertible and and should be "exact" ( you can transform integers to
integers and invert if you do everything right). In this case, it may be easier to
write an inverse wavelet transform and output the numerical differences between 
original and recovered sequences.

More to the point, at least verify that the suspect code block is really guilty and
try to disassemble it.

Also, as far as speed, look at something like FFTW ( you can find stuff on google).
They have lots of documentation and discussion posted in various places.
Or, the link I posted earlier to Intel site should help. Don't just count instructions
as memory access patterns can be a much bigger deal- think various shades or
virtual memory. 

> Date: Tue, 4 Dec 2007 10:19:42 +0530
> From: dhruvakm_at_[hidden]
> To: boost-users_at_[hidden]
> Subject: Re: [Boost-users] C++ Performance
>
> Hi,
>
> On 12/1/07, nisha kannookadan  wrote:
>>> "diff " would work if you could get the same formats and precisions.
>>
>> What is "diff" ?
>
>>From my understanding:
>
> If you can write the results of your computation into a file, write
> the output from MATLAB and then from your C++ program. Make sure you
> have follow the same order in writing the data to a file (with same
> formatting like spaces/newlines...)
> Use a program like GNU diff/kdiff3/windiff on the two output files you
> have to find the differences between them. Ideally, you should not see
> any difference. If you do notice a difference, check if the difference
> is negligible (you have to decide the precision you are expecting).
>
> The idea behind this is:
> A drive to improve performance _must_ not degrade the correctness of
> the solution.
>
> -dky
>
> --
> Contents reflect my personal views only!
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