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temp contains an 8 point fft. >>temp = fft(x,num_pts) temp = Columns 1 through 5 0.0000 -0.0000 - 4.0000i 1.4142 + 1.4142i -0.0000 + 0.0000i -0.0000 Columns 6 through 8 -0.0000 - 0.0000i 1.4142 - 1.4142i -0.0000 + 4.0000i >>angle_fft = angle(temp) angle_fft = 0 -1.5708 0.7854 1.5965 3.1416 -1.5965 -0.7854 1.5708 Qn) the 3 phase angles ( 1.5965 , 3.1416, -1.5965 ) should actually be equal to zero, since the corresponding temp elements are (-0.0000 + 0.0000i , -0.0000 , -0.0000 - 0.0000i ) , why is the angle function returning ( 1.5965 , 3.1416, -1.5965 ) instead of 0 ? How to fix this. thanks thanks |
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angle funtion doesnt give right phase angles
Started by ●October 9, 2004
Reply by ●October 11, 20042004-10-11
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Mr. DooDoo 90210- > temp contains an 8 point fft. > >>temp = fft(x,num_pts) What's in temp you've printed. What's in num_pnts? > temp = > Columns 1 through 5 > > 0.0000 -0.0000 - 4.0000i 1.4142 + 1.4142i -0.0000 + > 0.0000i -0.0000 > > Columns 6 through 8 > > -0.0000 - 0.0000i 1.4142 - 1.4142i -0.0000 + 4.0000i > > >>angle_fft = angle(temp) > > angle_fft = > > 0 -1.5708 0.7854 1.5965 3.1416 -1.5965 -0.7854 1.5708 > > Qn) the 3 phase angles ( 1.5965 , 3.1416, -1.5965 ) should > actually be equal to zero, since the corresponding temp elements are > (-0.0000 + 0.0000i , -0.0000 , -0.0000 - 0.0000i ) , why is > the angle function returning ( 1.5965 , 3.1416, -1.5965 ) > instead of 0 ? > How to fix this. A "negative zero" looks interesting. If you print that to more precision, my guess is that you find some very small value there. In which case arctan(-small value/zero) would be pi/2. -Jeff |
