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+math/fft_partial.m

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+% FFT_PARTIAL apply fft only on smaller blocks (important for GPU)
+% 
+%  x = fft_partial(x,fft_axis,split_axis, split, inverse = false)
+% 
+% Inputs: 
+%   **x         - input array 
+%   **fft_axis  - axis along which is performed FFT 
+%   **split_axis - axis along which is the array split 
+%
+%  *optional*
+%   **split - number of blocks to split the array before FFT to save the memory 
+%   **inverse - if true, use ifft intead of fft 
+% 
+% *returns*
+%   ++x       fft transformed array 
+
+    
+    
+%*-----------------------------------------------------------------------*
+%|                                                                       |
+%|  Except where otherwise noted, this work is licensed under a          |
+%|  Creative Commons Attribution-NonCommercial-ShareAlike 4.0            |
+%|  International (CC BY-NC-SA 4.0) license.                             |
+%|                                                                       |
+%|  Copyright (c) 2017 by Paul Scherrer Institute (http://www.psi.ch)    |
+%|                                                                       |
+%|       Author: CXS group, PSI                                          |
+%*-----------------------------------------------------------------------*
+% You may use this code with the following provisions:
+%
+% If the code is fully or partially redistributed, or rewritten in another
+%   computing language this notice should be included in the redistribution.
+%
+% If this code, or subfunctions or parts of it, is used for research in a 
+%   publication or if it is fully or partially rewritten for another 
+%   computing language the authors and institution should be acknowledged 
+%   in written form in the publication: “Data processing was carried out 
+%   using the “cSAXS matlab package” developed by the CXS group,
+%   Paul Scherrer Institut, Switzerland.” 
+%   Variations on the latter text can be incorporated upon discussion with 
+%   the CXS group if needed to more specifically reflect the use of the package 
+%   for the published work.
+%
+% A publication that focuses on describing features, or parameters, that
+%    are already existing in the code should be first discussed with the
+%    authors.
+%   
+% This code and subroutines are part of a continuous development, they 
+%    are provided “as they are” without guarantees or liability on part
+%    of PSI or the authors. It is the user responsibility to ensure its 
+%    proper use and the correctness of the results.
+
+
+function x = fft_partial(x,fft_axis,split_axis, split, inverse)
+    persistent current_gpu 
+    
+    import math.*
+    
+    if nargin < 5
+        inverse = false; % do inverse fft 
+    end
+    
+    if nargin < 4 || isempty(split)
+        % auto estimation of the split 
+        mem_req = numel(x)*8 * log2(size(x,fft_axis)); 
+        if isa(x,'gpuArray')
+            % move directly to complex to include the expected memore requirements 
+            x = complex(x);
+            if isempty(current_gpu) || isnan(current_gpu.AvailableMemory)
+                current_gpu = gpuDevice; 
+            end
+            split = ceil(mem_req / current_gpu.AvailableMemory); 
+        else
+            if mem_req < 50e9
+                % assume to have at least 50GB ram free ...
+                split = 1; 
+            else
+                avail_mem = utils.check_available_memory * 1e6;
+                split = ceil(mem_req /avail_mem); 
+            end
+        end
+    end
+
+
+    
+    if all(split == 1)
+        if inverse
+           x = ifft(x,[],fft_axis);
+        else
+           x = fft(x,[],fft_axis);
+        end
+        return 
+    end
+    
+    
+    % check GPU memory 
+    Np = size(x);
+    Nps = Np;
+    Nps(split_axis) = ceil(Nps(split_axis)  / split);
+
+    ind = {':', ':',':'};
+    for i = 1:split
+        ind{split_axis} = (1+(i-1)*Nps(split_axis)): min(Np(split_axis), i*Nps(split_axis));
+        x_tmp = x(ind{:});
+        if ~inverse
+            x_tmp = fft(x_tmp, [], fft_axis);  % avoid additonal memory assignment
+        else
+            x_tmp = ifft(x_tmp, [], fft_axis); 
+        end
+        x(ind{:}) = x_tmp;
+    end
+    
+end