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Fast Fourier Transformation (FFT) in .NET (C# and Visual Basic)
The recommended way of computing FFTs is to utilize the static builtin functions of the
1  dimensional Fourier Transforms  

Computes the onedimensional fft on columns of A. If A is a ndimensional array, the operation is performed along the first nonsingleton dimension and repeated for all subsequent dimensions. The output will be a complex array, having the same size as A. For A of element type 

Same as 

Computes the onedimensional inverse fft on columns of A. The function is the counterpart to 

Computes the onedimensional inverse fft along the 'dim' dimension of A. The function is the counterpart to 

Computes the onedimensional inverse fft along the first nonsingleton dimension of A. A must be complex hermitian. This, f.e. is true, if A is the result of a FFT on real data. Since the result of transforming complex hermitian arrays is concidered real anyway, the function returns a real array directly. Internally the computation is speed up by ommiting the complex parts accordingly.  
Computes the onedimensional inverse fft of complex hermitian data along the dimension ' 

2  dimensional Fourier Transforms  
Computes the twodimensional fft on columns of A. If A is a ndimensional array, the operation is performed along the first two dimensions and repeated for all subsequent higher dimensions. The output will be a complex array, having the same size as A. For A of element type 

Same as 

Computes the twodimensional inverse fft on the first two dimensions of A. The function is the counterpart to 

Computes the twodimensional inverse fft for the resized version of A. This function is the counterpart to 

Computes the twodimensional inverse fft along the first two dimensions of A. A must be complex hermitian in those dimensions. This, f.e. is true, if A is the result of a twodimensional FFT of real array elements ( 

Computes the twodimensional inverse fft of complex hermitian data in A along the first two dimensions. This function returns a real array.  
n  dimensional Fourier Transforms  
Computes the ndimensional fft on the first n dimensions of A. If n is less than the number of dimensions of A, the operation is repeated for all subsequent higher dimensions. The output will be a complex array, having the same size as A. For A of element type 

Same as 

Computes the n dimensional inverse fft on first n dimensions of A. The function is the counterpart to 

Computes the n dimensional inverse fft for the resized version of A. This function is the counterpart to 

Computes the n dimensional inverse fft along the first n dimensions of A. A must be complex hermitian in those dimensions. This, f.e. is true, if A is the result of a ndimensional FFT on real data elements ( 

Computes the n dimensional inverse fft of complex hermitian data in A along the first n dimensions. This function returns a real array. One has to make sure, the resized version of A is complex hermitian. Otherwise the result is undefined. 