Bug 164466

Summary:	The Peak of the Kst Amplitude Spectrum is lower than the Amplitude Spectrum in Octave
Product:	[Applications] kst	Reporter:	Yiwen Mao <yiwenv>
Component:	general	Assignee:	kst
Status:	RESOLVED NOT A BUG
Severity:	normal
Priority:	NOR
Version:	1.x
Target Milestone:	---
Platform:	unspecified
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:
Attachments:	This kst file has the plot of the amplitude spectrum described in bug report The resulting amplitude spectrum from the Octave the mfile used to plot the amplitude spectrum in octave kst file of the simpler case

Description Yiwen Mao 2008-06-19 19:51:56 UTC

Version:           1.7.0 (using KDE 4.0.1)
Installed from:    Unspecified
Compiler:          Fedora 6 
OS:                Linux

Problem: Use both Octave and Kst to plot the amplitude spectrum of the following function
f=(sin(5*pi*t)).^4+(cos(5*pi*t)).^5,where t ranges from 0 to 3

In Kst, the spectrum is set up as shown below:
The FFT length is 2^7
The sample rate is 265.99
The resulting spectrum is not viewed by an apodization function.
The mean is not removed

In Octave, the following is calculated before plotting the spectrum:
N=2^7;
t=linspace(0,3,N); %t is a vector with N linearly spaced elements between 0 and 3
Ts=t(2)-t(s); %sampling period
Ws=2*pi/Ts; %sampling rate = 265.99
W=Ws*(-N/2:(N/2)-1)/N; %frequecny vector

Comment 1 Yiwen Mao 2008-06-19 19:56:23 UTC

Created attachment 25459 [details]
This kst file has the plot of the amplitude spectrum described in bug report

Comment 2 Yiwen Mao 2008-06-19 19:58:11 UTC

Created attachment 25460 [details]
The resulting amplitude spectrum from the Octave

Comment 3 Yiwen Mao 2008-06-19 20:06:43 UTC

Created attachment 25462 [details]
the mfile used to plot the amplitude spectrum in octave

Comment 4 Andrew Walker 2008-06-19 21:09:41 UTC

Created attachment 25464 [details]
kst file of the simpler case

The attached uses a simple 2*cos(t) function for about 8 cycles to calculate
the amplitude spectrum. Kst identifies the single peak in the amplitude
spectrum as 2.0

Comment 5 Andrew Walker 2008-06-19 23:12:20 UTC

The Kst values look okay.