hello,
I use the ippsStdDev_32f with "ippAlgHintFast" mode to calculate standard deviation of a vector. It seems than the standard deviation value is zero when the length of vector is greater than 10000(maybe 8192). For comparison, the standard deviation value in ippsMeanStdDev_32f is not zero with the same parameters.
It was described in the document that "ippAlgHintFast is faster but less accurate calculation". However, is it bug to have a result of zero in ippsStdDev_32f？
I am using IPP version 2021.7.0, windows10 1809, visual studio 2019.
I tested three hint mode of both two functions in c++:
int iSrcLength = 10000;
float fStdDevValue = 123.0f; //initialize
float fMeanValue = 123.0f; //initialize
std::unique_ptr<float[]> pInput(new float[iSrcLength]);
for (int idx = 0; idx < iSrcLength; ++idx)
{
pInput[idx] = static_cast<float>(idx);
}
std::cout << "the length of the vector is: " << iSrcLength << std::endl;
if (ippStsNoErr != ippsStdDev_32f(pInput.get(), iSrcLength, &fStdDevValue, ippAlgHintNone))
{
std::cout << "ERROR:ippsStdDev_32f" << std::endl;
}
std::cout << "StdDev Value in ippsStdDev_32f() with ippAlgHintNone:" << fStdDevValue << std::endl;
if (ippStsNoErr != ippsStdDev_32f(pInput.get(), iSrcLength, &fStdDevValue, ippAlgHintFast))
{
std::cout << "ERROR:ippsStdDev_32f" << std::endl;
}
std::cout << "StdDev Value in ippsStdDev_32f() with ippAlgHintFast:" << fStdDevValue << std::endl;
if (ippStsNoErr != ippsStdDev_32f(pInput.get(), iSrcLength, &fStdDevValue, ippAlgHintAccurate))
{
std::cout << "ERROR:ippsStdDev_32f" << std::endl;
}
std::cout << "StdDev Value in ippsStdDev_32f() with ippAlgHintAccurate:" << fStdDevValue << std::endl;
if (ippStsNoErr != ippsMeanStdDev_32f(pInput.get(), iSrcLength, &fMeanValue, &fStdDevValue, ippAlgHintNone))
{
std::cout << "ERROR:ippsMeanStdDev_32f" << std::endl;
}
std::cout << "StdDev Value in ippsMeanStdDev_32f() with ippAlgHintNone:" << fStdDevValue << std::endl;
if (ippStsNoErr != ippsMeanStdDev_32f(pInput.get(), iSrcLength, &fMeanValue, &fStdDevValue, ippAlgHintFast))
{
std::cout << "ERROR:ippsMeanStdDev_32f" << std::endl;
}
std::cout << "StdDev Value in ippsMeanStdDev_32f() with ippAlgHintFast:" << fStdDevValue << std::endl;
if (ippStsNoErr != ippsMeanStdDev_32f(pInput.get(), iSrcLength, &fMeanValue, &fStdDevValue, ippAlgHintAccurate))
{
std::cout << "ERROR:ippsMeanStdDev_32f" << std::endl;
}
std::cout << "StdDev Value in ippsMeanStdDev_32f() with ippAlgHintAccurate:" << fStdDevValue << std::endl;
results:
the length of the vector is: 10000
StdDev Value in ippsStdDev_32f() with ippAlgHintNone:2886.9
StdDev Value in ippsStdDev_32f() with ippAlgHintFast:0
StdDev Value in ippsStdDev_32f() with ippAlgHintAccurate:2886.9
StdDev Value in ippsMeanStdDev_32f() with ippAlgHintNone:2886.9
StdDev Value in ippsMeanStdDev_32f() with ippAlgHintFast:2886.9
StdDev Value in ippsMeanStdDev_32f() with ippAlgHintAccurate:2886.9
