Data structures and spmd

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D W
D W 2019-10-24
编辑： Raag 2025-2-18
My code stores composite variables within data structures with a variable number of structure fields i.e.
Pool_Size = 3;
parpool(Pool_Size);
n=2;
for Cntr = 1:n
Comp_Variable = Composite();
for Pool_Cntr = 1:Pool_Size
Comp_Variable{Pool_Cntr} = rand(2,2);
end
Data_Struct(Cntr).Comp_Variable = Comp_Variable;
end
I need to pass these variables into functions within spmd i.e. of the form (pseudo code):
spmd
for Cntr = 1:n
Result = My_Function(Data_Struct(Cntr).Comp_Variable)
end
end
Obviously I can't directly index the structure fields due to transparency issues within spmd i.e.
spmd, Data_Struct(1).Comp_Variable, end
which will result in an invalid composite. The standard work around I have seen for other similar cases with structs or cell arrays is to specify new variables before entering the spmd data i.e.
Data1 = Data_Struct(1).Comp_Variable;
Data2 = Data_Struct(2).Comp_Variable;
spmd
Data1
Data2
end
where Data1, Data2 can now be passed into a function within the spmd without issue. However, if I have variable number of structure fields I can't think of good way to do this without resorting to the dreaded eval function to both define the new variable names and pass these to the function within spmd (in the later case the calls to eval would be done inside another function, again to adhere to the transparency rules for spmd). Does anybody have a better approach to accessing the composite vbariables within the spmd without having to define each one explicitely before the spmd block?
Any help would be greatly appreciated.

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回答（1 个）

Raag
Raag 2025-2-18
编辑：Raag 2025-2-18
Hi D W,
As per my understanding the issue you're facing stems from MATLAB's transparency rules within 'spmd', which prevents direct indexing of nested Composite fields. Defining separate variables manually isn't scalable, and using eval is not ideal.
As a workaround, you can nest Composite objects inside another Composite to manage your data effectively. Here's a brief example:
% Create a single Composite to hold all data
AllData_Comp = Composite();
for w = 1:Pool_Size
AllData_Comp{w} = {Data_Struct(1).Comp_Variable{w}, Data_Struct(2).Comp_Variable{w}};
end
The explanation of how it works is that by nesting, each worker has access to all necessary data without manual variable creation and ‘AllData_Comp’ is recognized within ‘spmd’ which avoids transparency errors.
For a better understanding of the above solution, refer to the following MATLAB documentations:
1. Composite Objects: https://www.mathworks.com/help/parallel-computing/composite.html
2. spmd: https://www.mathworks.com/help/parallel-computing/spmd.html
3. parpool: https://www.mathworks.com/help/parallel-computing/parpool.html

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