傅立叶变换

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a =

0 4 2 1 1 2 4 6

>> ia=ifft(a)

ia =

Columns 1 through 7

2.5000 0.4937 - 0.5152i -0.6250 - 0.1250i -0.7437 - 0.0152i -0.7500 -0.7437 + 0.0152i -0.6250 + 0.1250i

Column 8

0.4937 + 0.5152i

>> ib=[0,0,0,0,0,0,0,0]

ib =

0 0 0 0 0 0 0 0

>> ic=[ib,ic]
??? Undefined function or variable "ic".

>> ic=[ia,ib]

ic =

Columns 1 through 7

2.5000 0.4937 - 0.5152i -0.6250 - 0.1250i -0.7437 - 0.0152i -0.7500 -0.7437 + 0.0152i -0.6250 + 0.1250i

Columns 8 through 14

0.4937 + 0.5152i 0 0 0 0 0 0

Columns 15 through 16

0 0

>> c=fft(ic)

c =

Columns 1 through 7

0 2.5000 + 1.4899i 4.0000 2.5000 - 1.5371i 2.0000 2.5000 - 1.0723i 1.0000

Columns 8 through 14

2.5000 + 0.1492i 1.0000 2.5000 + 1.4243i 2.0000 2.5000 + 2.1584i 4.0000 2.5000 + 1.1581i

Columns 15 through 16

6.0000 2.5000 - 3.7705i
上面的a是频域的一个8点序列，然后经过ifft得到时域的数据ia，把ia补0扩展成16点，然后用fft变化回频域，这个频域只和原来频域值数据什么关系呢？