Parfor: Converting broadcast variables into temporary variables or sliced variables

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Brandon
Brandon 2021-5-18
评论： Walter Roberson 2021-5-18
Is there a difference in efficiency if I just assign a broadcast varible to a temporary variable inside a parfor loop vs re-writing it as a sliced variable that is indexed the same as the main index of the parfor loop? Matlab does not categorize it as a broadcast variable either way, but I'm not sure if the temporary variable method still avoids sending more data than is necesary to workers.

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Matt J
Matt J 2021-5-18
编辑：Matt J 2021-5-18
Temporary variables are not sent to the workers. They are created on the workers (and are destroyed there).
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Brandon
Brandon 2021-5-18
Thanks. Follow up question: Suppose that the example above is modifed slightly so that the temporary variable is always assigned a constant and the broadcast variable is never used:
parfor ih=1:10
if ih>0
a=0;
else
a=x;
end
store{ih} = f(a); % some operations on a
end
Does the broadcast variable, x, still get sent to every worker?
Walter Roberson
Walter Roberson 2021-5-18
Yes, the broadcast variable will (probably) be sent. MATLAB does some static flow analysis, but you cannot count on it being advanced enough to be able to reason that ih>0 will always be true.

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