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Re: [Discuss-gnuradio] Cumsum block on GRC


From: Nick Foster
Subject: Re: [Discuss-gnuradio] Cumsum block on GRC
Date: Sat, 07 May 2011 16:57:19 +0200

On Sat, 2011-05-07 at 15:53 +0100, Tom Rondeau wrote:
> On Sat, May 7, 2011 at 3:44 PM, mehmet kabasakal
> <address@hidden> wrote:
>         Hi List,
>         
>         I am trying to write a block, that finds the cumulative sum of
>         the points.
>         But when i run the block on GRC, the output of the block
>         becomes as in
>         the attached figure. It wraps for a period of time. I expect
>         it to go
>         negatively downwards. Because i am accumulating negative
>         values. I
>         couldn't understand the reason. Is there something missing in
>         the
>         code. The c++ code of the block is attached also.
>         
>         Thanks for the help!
>         Mehmet.
> 
> 
> 
> Mehmet,
> It looks like it's because you are setting out[0] = 0 before entering
> the for loop in your work function. This will then reset the counter
> every time you enter work.

I'm pretty sure it won't work even if you remove that call. You can't
count on out[0] having any sort of reasonable value when invoking the
work call. Try saving the cumulative sum in a private member variable of
your class, initialize it to 0 in your constructor, and setting out[0]
to that saved value when starting each work function call.

--n

> 
> 
> Tom
> 
> 
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