**PURPOSE**- Computes the self-correlation function of an image/volume by using the Fourier transform relationship. Example.

**SEE ALSO****AC N**[Auto Correlation - Normalized ||] **AC S**[Self Correlation ||] **AC MS**[Auto Correlation - Masked and normalized ||] **CC**[Cross Correlation ||] **CC N**[Cross Correlation - Normalized ||] **CN**[Convolution ||] **CN N**[Convolution - Normalized ||] **FT**[Fourier Transform ||]

**USAGE**- .OPERATION: AC NS

- .INPUT FILE: PIC001

[Enter the name of the image/volume to be self-correlated.].OUTPUT FILE: ACF001

[Enter name of the file which will contain the self-correlation coefficients.]

**NOTES**

- On completion of this operation, the output file will contain
the self-correlation function.

The origin is at (INT(NX/2) + 1, INT(NY/2) + 1, INT(NZ/2) + 1).

The SCF is not normalized. - The type of input data can be either real or Fourier.
- The self-correlation function is defined in "Correlation functions revisited", M. van Heel, M. Schatz, E. Orlova. Ultramicroscopy, 46, (1992) 307-316; as inverse Fourier transform of the square root of the modulus of the Fourier transform of the input image.

**SUBROUTINES**- FMRS_2, FMRS_2R, FFTMCF, FMRS_1, FMRS_3, FMRS_3R, ACRS_2S, ACRS_3S

**CALLER**- CORR1

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