memoize => Save/Restore Cache

Hi,

would it be possible to Save and Restore the memoize Cache?

Calculating the cache would take 4min and it would be easier to load it from a file since i use it daily.

I found this to read the cache but nothing to restore it

>> s = stats(mfCR);

>> s.Cache.Inputs{:};

Thanks for your responds

Benno

Answer 1

[Jan]

There is no documented way to store the cache. But it is cheap to create a look-up table for your function and store it manually. This uses GetMD5 for hashing the inputs:

function varargout = FcnLUT(fcn, varargin)
% Cache output of function for specific input
% varargout = FcnLUT(fcnName, varargin)
% INPUT:
%   fcn:  Function handle or name of the function as CHAR vector.
%         Special commands: 'clear', 'save', 'load' to manage the cache.
%   varargin: Arguments of the function.
% OUTPUT:
%   Same output as: fcnName(varargin{:})
%
% EXAMPLE:
%   tic; x = FcnLUT(@(x,y) exp(x:y), 1, 1e8); toc
%   tic; x = FcnLUT(@(x,y) exp(x:y), 1, 1e8); toc
% The 2nd call is much faster, because the output is copied from the cache.
% Huge input arguments slow down the caching, because calculating the hash of
% the data is expensive. Example:
%   tic; x = FcnLUT(@exp, 1:1e8); toc  % Tiny advantage only!
% 
% Tested: Matlab 2009a, 2015b(32/64), 2016b, 2018b, Win10
% Author: Jan Simon, Heidelberg, (C) 2023
% Dependency: https://www.mathworks.com/matlabcentral/fileexchange/25921-getmd5

% $License: BSD (use/copy/change/redistribute on own risk, mention the author) $
% History:
% 001: 13-Jan-2023 17:24, First version.

% Initialize: ==================================================================
persistent LUT
if isempty(LUT)
   LUT = struct();
end

% Manage the cache: ============================================================
if nargin == 1
   dataFile = fullfile(fileparts(mfilename('fullpath')), 'FcnLUT.mat');
   switch lower(fcn)
      case 'clear'
         LUT = struct();
      case 'save'
         save(dataFile, '-struct', 'LUT');
      case 'load'
         if isfile(dataFile)
            LUT = load(dataFile);
         end
      otherwise
         error(['Jan:', mfilename, ':BadCommand'], ...
            'Unknown command: %s', fcn);
   end
   return;
end

% Get answer from cache or perform the calculations: ===========================
H = ['H_', GetMD5({fcn, varargin}, 'Array', 'hex')];
if isfield(LUT, H)
    varargout = LUT.(H);
else
    [varargout{1:nargout}] = feval(fcn, varargin{:});
    LUT.(H)                = varargout;
end

end

Finally, this is a replacement for the memoize() function.