How not to reload persistent variables twice?

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Mr M.
Mr M. 2017-7-21
编辑： Jan 2017-7-21
I wnat to use persistent variables to speed up, so I want to genrate data, and make it persistent at the first call, but how to check next time, that this is not the first call, and I dont want to genrate the data again?

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采纳的回答

Walter Roberson
Walter Roberson 2017-7-21
if isempty(VariableName)
... calculate initial value for variable
end

更多回答（1 个）

Jan
Jan 2017-7-21
编辑：Jan 2017-7-21
This is explained in the documentation: doc persistent:
function arrayToXLS(A, xlsfile, x1, x2)
persistent dblArray;
if isempty(dblArray)
disp 'Writing spreadsheet file ...'
xlswrite(xlsfile, A);
end
Undefined persistent variables are empty. If your real data might be empty also, use a persistent flag in addition:
persistent Data initialized
if isempty(initialized)
initialized = true;
Data = <what eve you want, even empty array>
end

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