Problem with ippsCrossCorr

jenni80 — Tue, 02 Dec 2008 15:58:39 GMT

Hi,

I'm using the trial version of the Ipps libraries and i have difficulties with the result of the function IppsCrossCorr_32f()

in the FAQ sheet the Usage is explained as follows :

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

void crossCorr(void) {
#undef LEN
#define LEN 11
Ipp32f win[LEN], y[LEN];
IppStatus st;
ippsSet_32f (1, win, LEN);
ippsWinHamming_32f_I (win, LEN);
st = ippsCrossCorr_32f (win, LEN, win, LEN, y, LEN, -(LEN-1));
printf_32f(cross corr =, y,7,st);
}
Output:
cross corr = 0.006400 0.026856 0.091831 0.242704 0.533230
1.009000 1.672774
Matlab* analog:
>> x = hamming(11)'; y = xcorr(x,x); y(1:7)

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

so i wrote a code (snippet) as follows:

const int SIZE = 100;

Ipp32f *temp = new Ipp32f[SIZE];

// Then i load some data from disc to "temp"
Ipp32f *temp1 = new Ipp32f[SIZE];
Ipp32f *temp2 = new Ipp32f[1];

IppStatus st;
ippsWinHamming_32f(temp,temp1,SIZE); // I don't want to manipulate my original signal
st = ippsCrossCorr_32f(temp1,30,temp1+40,30,temp2,1,30);

// i just want one cross correlation on a certain part of the same signal
cout << temp2[0] << "-" << st <

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

But the output of temp2[0] is always -0.00132704 no matter what data i load into temp. the value of "st" is -6 which tells me just nothing, but maybe you.

In my real code i use the cross_corr() function on one signal more than once, going step by step over a very long signal seqence checking every time a small part of the signal to find a maximum value. So the real code is a bit more complex than this .. but i checked many parts of my code. The input signal changes every loop , i used different sources for the temp array. No matter what i do the output is always -0.00132704.

I suppose the fault is made by me but i don't know where i did something wrong, so please can you give me some advice ?

Thanks in advance ...

Re: Problem with ippsCrossCorr

Vladimir_Dudnik — Wed, 03 Dec 2008 08:51:01 GMT

Hello,

there is special function in IPP (ippGetStatusString) which translate IppStatus value to textual string (of course you can do the same just looking at ippdefs.h file forenumerator value.

I would recommend youto look at function description in IPP manual, it might help to understand function behavior.

Regards,
Vladimir

Re: Problem with ippsCrossCorr

jenni80 — Thu, 04 Dec 2008 16:53:23 GMT

Quoting - vdudnik

Hello,

there is special function in IPP (ippGetStatusString) which translate IppStatus value to textual string (of course you can do the same just looking at ippdefs.h file forenumerator value.

I would recommend youto look at function description in IPP manual, it might help to understand function behavior.

Regards,
Vladimir

Hi.

thanks that did it, i had forgotten some brackets and the function got some wrong parameters. Now it doeas what is says .. :-)

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Problem with ippsCrossCorr

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Re: Problem with ippsCrossCorr