test_fft.m running
a=
         0    0.7071    1.0000    0.7071         0   -0.7071   -1.0000   -0.7071
b=fft(a)=
  Columns 1 through 4
        0                  0 - 4.0000i        0                  0 + 0.0000i
  Columns 5 through 8
        0                  0 - 0.0000i        0                  0 + 4.0000i
abs(b)=
         0    4.0000         0    0.0000         0    0.0000         0    4.0000
fftshift(abs(b))=
         0    0.0000         0    4.0000         0    4.0000         0    0.0000
c=ifft(b)=
         0    0.7071    1.0000    0.7071         0   -0.7071   -1.0000   -0.7071
abs(c)=
         0    0.7071    1.0000    0.7071         0    0.7071    1.0000    0.7071