log2 function has incorrect help text

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Michael Wagner
Michael Wagner 2017-2-21
评论： Steven Lord 2017-2-21
The following help text is incorrect: [F,E] = log2(X) for each element of the real array X, returns an array F of real numbers, usually in the range 0.5 <= abs(F) < 1, and an array E of integers, so that X = F .* 2.^E.
In fact there is only ONE array F and ONE array E for a real array X, such that for each element X(i), X(i) = F(i) .* 2.^E(i).
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Steven Lord
Steven Lord 2017-2-21
Your statement is not quite true. Consider the case where X is Inf, -Inf, or NaN. I don't have a reference link for the ANSI C frexp function cited in the Tips section of the log2 documentation page but the C++ std::frexp() function says that for nonfinite values of arg, the nonfinite value is returned by std::frexp and "an unspecified value is stored in *exp".
The documentation should probably list what this function returns for non-finite values like it documents the behavior for X = 0. I've asked the documentation staff to take advantage of your feedback to make this change.

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Adam
Adam 2017-2-21
There is a 'Was this topic helpful?' question at the bottom of each help page. Click 'No' on that and you get a chance to give feedback which Mathworks staff will generally respond to fairly quickly.

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