fftshift
Rearranges an array in a manner similar to Matlab's fftshift function.
Available in version 6.3.0 and later.
Prototype
function fftshift ( x : numeric, mode [1] : integer ) return_val : same size, shape and type as x
Arguments
xA vector or multidimensional array. If there are two or more dimensions, the two rightmost dimensions will be the rearranged.
modeType of rearrangement (shift) to be performed.
Return value
An array of the same size, type and shape as x with the elements rearranged.
Description
See the Matlab description of fftshift. Also, see the examples below.
See Also
reshape, reshape_ind, conform, conform_dims, ndtooned, onedtond
Examples
Example 1
Using fftshift on a vector (i.e., a one-dimensional array).
f = (/ 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, -0.5, -0.4, -0.3, -0.2, -0.1 /) fshift = fftshift(f, 0) print(fshift)
This would yield 0.0 in the middle.
fshift = (/ -0.5, -0.4, -0.3, -0.2, -0.1, 0.0, 0.1, 0.2, 0.3, 0.4, 0.5/)
Example 2
Using fftshift on an even number of rows and columns:
nrow = 6
ncol = 6
N = nrow*ncol
a = onedtond(fspan(1,N,N), (/nrow,ncol/))
print(" ")
print("--- Original Array ---")
write_matrix (x, ncol+"f7.2", False)
x = fftshift(a, 0)
print("---mode= 0 quadrant shift")
write_matrix (x, ncol+"f7.2", False)
y = fftshift(a, 1)
print("---mode= 1 column shift")
write_matrix (y, ncol+"f7.2", False)
z = fftshift(a,-1)
print("---mode= -1 row shift")
write_matrix (y, ncol+"f7.2", False)
This would yield:
original array: a (6,6)
1.00 2.00 3.00 4.00 5.00 6.00
7.00 8.00 9.00 10.00 11.00 12.00
13.00 14.00 15.00 16.00 17.00 18.00
19.00 20.00 21.00 22.00 23.00 24.00
25.00 26.00 27.00 28.00 29.00 30.00
31.00 32.00 33.00 34.00 35.00 36.00
---mode= 0 quadrant shift: x
22.00 23.00 24.00 19.00 20.00 21.00
28.00 29.00 30.00 25.00 26.00 27.00
34.00 35.00 36.00 31.00 32.00 33.00
4.00 5.00 6.00 1.00 2.00 3.00
10.00 11.00 12.00 7.00 8.00 9.00
16.00 17.00 18.00 13.00 14.00 15.00
---mode= 1 columns shift: y
4.00 5.00 6.00 1.00 2.00 3.00
10.00 11.00 12.00 7.00 8.00 9.00
16.00 17.00 18.00 13.00 14.00 15.00
22.00 23.00 24.00 19.00 20.00 21.00
28.00 29.00 30.00 25.00 26.00 27.00
34.00 35.00 36.00 31.00 32.00 33.00
---mode=-1 row shift: z
19.00 20.00 21.00 22.00 23.00 24.00
25.00 26.00 27.00 28.00 29.00 30.00
31.00 32.00 33.00 34.00 35.00 36.00
1.00 2.00 3.00 4.00 5.00 6.00
7.00 8.00 9.00 10.00 11.00 12.00
13.00 14.00 15.00 16.00 17.00 18.00
==================================================
Example 3
Using fftshift on an even number of rows and an odd number of columns:
nrow = 6
ncol = 5
N = nrow*ncol
The results are:
--- Original Array (6,5) --- 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00 19.00 20.00 21.00 22.00 23.00 24.00 25.00 26.00 27.00 28.00 29.00 30.00 ---mode= 0 quadrant shift 19.00 20.00 16.00 17.00 18.00 24.00 25.00 21.00 22.00 23.00 29.00 30.00 26.00 27.00 28.00 4.00 5.00 1.00 2.00 3.00 9.00 10.00 6.00 7.00 8.00 14.00 15.00 11.00 12.00 13.00 ---mode= 1 column shift 4.00 5.00 1.00 2.00 3.00 9.00 10.00 6.00 7.00 8.00 14.00 15.00 11.00 12.00 13.00 19.00 20.00 16.00 17.00 18.00 24.00 25.00 21.00 22.00 23.00 29.00 30.00 26.00 27.00 28.00 ---mode=-1 row shift 16.00 17.00 18.00 19.00 20.00 21.00 22.00 23.00 24.00 25.00 26.00 27.00 28.00 29.00 30.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00
Example 4
Using fftshift on an odd number of rows and an even number of columns:
nrow = 5
ncol = 6
N = nrow*ncol
The results are:
--- Original Array (5,6)--- 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00 19.00 20.00 21.00 22.00 23.00 24.00 25.00 26.00 27.00 28.00 29.00 30.00 ---mode=0 quadrant shift 22.00 23.00 24.00 19.00 20.00 21.00 28.00 29.00 30.00 25.00 26.00 27.00 4.00 5.00 6.00 1.00 2.00 3.00 10.00 11.00 12.00 7.00 8.00 9.00 16.00 17.00 18.00 13.00 14.00 15.00 ---mode=1 column shift 4.00 5.00 6.00 1.00 2.00 3.00 10.00 11.00 12.00 7.00 8.00 9.00 16.00 17.00 18.00 13.00 14.00 15.00 22.00 23.00 24.00 19.00 20.00 21.00 28.00 29.00 30.00 25.00 26.00 27.00 ---mode=-1 row shift 19.00 20.00 21.00 22.00 23.00 24.00 25.00 26.00 27.00 28.00 29.00 30.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00
Example 5
Using fftshift on an odd number of rows and columns:
nrow = 5
ncol = 5
N = nrow*ncol
The results are:
--- Original Array --- 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00 19.00 20.00 21.00 22.00 23.00 24.00 25.00 ---mode= 0 quadrant shift 19.00 20.00 16.00 17.00 18.00 24.00 25.00 21.00 22.00 23.00 4.00 5.00 1.00 2.00 3.00 9.00 10.00 6.00 7.00 8.00 14.00 15.00 11.00 12.00 13.00 ---mode= 1 column shift 4.00 5.00 1.00 2.00 3.00 9.00 10.00 6.00 7.00 8.00 14.00 15.00 11.00 12.00 13.00 19.00 20.00 16.00 17.00 18.00 24.00 25.00 21.00 22.00 23.00 ---mode=-1 row shift 16.00 17.00 18.00 19.00 20.00 21.00 22.00 23.00 24.00 25.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00