MATLAB: Variable classification in Parfor loop

Parallel Computing Toolbox

Hi all –

I know this type of question has been asked many times, but I simply can't figure out how to translate my code to work. Very simply: – I have a large cell called "masterData", which merely holds my final data – In a parfor loop, I am performing an analysis that yields three large arrays rt, xo, and no. – I'd like to store the three large arrays in the masterData cell together with the sample name:

masterData=cell(20,1);
parfor i=1:20
%analysis here. Yields rt, xo, no
masterData{i,1:4}={name rt xo no};
end

I get the error "Error: The variable masterData in a parfor cannot be classified." I'm sure this is an easy fix relating to how masterData is populated. Any help is appreciated. Thanks,

Tristan

Best Answer

rt = 3;
xo = pi;
no = 2;
name = 'Sean';
masterData=cell(20,4);
parfor i=1:20
  %analysis here. Yields rt, xo, no
  masterData(i,:)={name rt xo no};
end

You index into masterData with columns 1:4 and curly braces yet the preallocated cell is a 20x1.

The 1:4 cannot be used because of this:

Form of Indexing. Within the list of indicesfor a sliced variable, one of these indices is of the form i, i+k, i-k, k+i,or k-i, where i is the loopvariable and k is a constant or a simple (nonindexed)broadcast variable; and every other index is a constant, a simplebroadcast variable, colon, or end.

http://www.mathworks.com/help/releases/R2013a/distcomp/advanced-topics.html#brdsfkm-1

Related Solutions

MATLAB: Am I unable to assign values to matrix blocks like A(10:20,i) inside the PARFOR loop in Parallel Computing Toolbox 4.1 (R2009a)

This error message obtained is the expected behavior when using PARFOR loops in Parallel Computing Toolbox 4.1 (R2009a).

PARFOR loops enforce stringent conditions on variables and expressions that appear in the loop body. As per the documentation of PARFOR, the variable A will be treated as a sliced variable as its value can be broken up into segments, each of which can be operated on separately by different workers.

The rules for indexing a sliced variable clearly state that within the list of indices for a sliced variable, one of these indices is of the form i, i+k, i-k, k+i, or k-i, where i is the loop variable and k is a constant or a simple (nonindexed) variable; and every other index is a constant, a simple variable, colon, or end.

Hence using an index of the form

 A(2:4, i)

is not permitted.

If the indices to be extracted are known apriori, the following workaround can be used

A = rand(10, 10);
b = (2:4);
parfor i = 1:4
      A(b, i) = ones(3, 1);
end

The above code snippet adheres to the conditions imposed on sliced variables.

MATLAB: Set class property only once

It sounds like you want a singleton property. This is how I'd designed it. As commented in Steven's answer, this doesn't and should not involve inheritence:

classdef MasterConfiguration < handle  %handle require so it can modify its own properties
    properties (SetAccess = private)
        MasterData
    end
    methods
        function this = MasterConfiguration() %constructor
            this.Initialise();  %Initialise 
        end
        function Initialise(this)  %Actual initialisation code. Decoupled from the constructor, so it can be reinitialised as needed
            %... initialisation code
        end
    end
end

classdef MasterDataUser  %can be handle or value class depending on needs
    properties (Constant)
        MasterDataConfiguration = MasterConfiguration;  %singleton object shared by all instances
    end
    methods
        %...
        function ReinitialiseMasterData(this)  %in case MasterData need to be reread
            this.MasterDataConfiguration.Initialise();  %all instances of MasterDataUser will see the newly initialised MasterConfiguration
        end
    end
end

If several classes need access to the same shared MasterData, then they must derive from MasterDataUser not from MasterConfiguration.

Best Answer

Related Solutions

MATLAB: Am I unable to assign values to matrix blocks like A(10:20,i) inside the PARFOR loop in Parallel Computing Toolbox 4.1 (R2009a)

MATLAB: Set class property only once

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