27/1/2001

rabbit 2001/1/2 PM 04:52 喂..

Benny 2001/1/2 PM 04:52 hihi

rabbit 2001/1/2 PM 04:52 what are u doing ar?

Benny 2001/1/2 PM 04:53 go to tutoring soon

rabbit 2001/1/2 PM 04:55 ic...

ai..poor me..個icq無端端死o左... restall都唔得

搞左好耐先用得番

rabbit 2001/1/2 PM 10:24 hi ar...

我想問下..matlab中..fft同fftshift的分別是什麼?

Benny 2001/1/2 PM 10:26 after fft, the spectrum will be:

123456654321

after fftshift

654321123456

normally, we want to execute fftshift after

fft

rabbit 2001/1/2 PM 10:28 咁plot magnitude spectrum是用fft?

Benny 2001/1/2 PM 10:29 abs()

rabbit 2001/1/2 PM 10:29 plot(abs(fft(y)))?

Benny 2001/1/2 PM 10:32 yes, it's better to specify how many pts u

want to plot.

eg to plot the magnitude against 4096 points

plot(linespace(-pi, pi, 4096), abs(...))

rabbit 2001/1/2 PM 10:36 I don't know how many points I should plot

Benny 2001/1/2 PM 10:36 see the spect, send ur program to me

rabbit 2001/1/2 PM 10:38 Here is the source code of x(t)

x=linspace(-4,4,400)

n=1

while n<=400

if (x(n)<=-2)

y(n)=0

elseif (x(n)<=0)

y(n)=x(n)+2

elseif (x(n)<=1)

y(n)=2

elseif (x(n)<3)

y(n)=2*cos(x(n)*pi/2)+2

elseif (x(n)>=3)

y(n)=2

end

n=n+1

end

plot(x,y)

Benny 2001/1/2 PM 10:42 it's difficult to understand,

send me the Q

Benny 2001/1/2 PM 10:45 if you run ur code, there must errors

rabbit 2001/1/2 PM 10:47 no error ar..

Benny 2001/1/2 PM 10:48 have graphs ploted?

rabbit 2001/1/2 PM 10:48 yep..

rabbit 2001/1/2 PM 10:48 I can't send file to u ar..

Benny 2001/1/2 PM 10:53 sorry,

ok, there is 400 points in your program

use

plot(x, y ) is ur time domain graph

Benny 2001/1/2 PM 10:53 r u using erg line?

rabbit 2001/1/2 PM 10:54 yep...

rabbit 2001/1/2 PM 11:02 so...also use 400 points in the magnitude

spectrum?

Benny 2001/1/2 PM 11:02 yes

rabbit 2001/1/2 PM 11:07 但出來的spectrum太密了．．有冇方法放大d?

Benny 2001/1/2 PM 11:08 try to plot more pts

rabbit 2001/1/2 PM 11:24 am I bothering u?

rabbit 2001/1/2 PM 11:33 am I bothering u?

Benny 2001/1/2 PM 11:33 no

Benny 2001/1/2 PM 11:42 if you plot the x(t) is right, so the fft of

it is also true

try plot after fftshift

rabbit 2001/1/2 PM 11:55 其實我set

x時做了linspace..plot時應該可以唔駛吧

Benny 2001/1/2 PM 11:58 yes, what's 1c?

rabbit 2001/1/2 PM 11:58 u told me to try plot fftshift ma..that't it

Benny 2001/1/2 PM 11:59 really??

rabbit 2001/1/2 PM 11:59 is that wrong??

Benny 2001/1/2 PM 11:59 send me ur code in .m file

Benny 2001/1/2 AM 12:04 sorry, I mean all ur codes, include fft...

rabbit 2001/1/2 AM 12:05 冇呀..我在command window run script之後才plot

Benny 2001/1/2 AM 12:07 ha ha...

y u do that??

just type in matlab edit mode, don't in

command mode

Benny 2001/1/2 AM 12:07 send to me later, offline a minute