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ISMEMBERF

15 Mar 2009 (Updated 13 Oct 2009)

Floating-point ISMEMBER (i.e., with round-off tolerance)

File Information
Description	Matlab ISMEMBER uses strict exact comparison between floats. The ISMEMBERF (note the "F") can tolerate some round off error. It is possible to configure the tolerance.'rows' option is also supported. Example: [tf, loc]=ismember(0.3, 0:0.1:1) % returns false [tf, loc]=ismemberf(0.3, 0:0.1:1) % return true
MATLAB release	MATLAB 7.2 (R2006a)
Zip File Content
Other Files	ismemberf.m, license.txt

Tags for This File
Everyone's Tags	float, ismember, numerical errors, round off
Tags I've Applied
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Comments and Ratings (4)
09 Oct 2009	David	PROBLEM: ismemberf([0 1 2], 0) will return [0 0 0]. It seems this is because line 263 will auto-configure tol to zero which causes unexpected results in ihi (line 274) that causes tf to be set incorrectly in line 276. WORK-AROUND: This behavior can be avoided if 'tol' is explicitly set when calling ismemberf().
10 Oct 2009	Bruno Luong	Thank you David for pointing out the bug. I better workaround IMO is change the line #257 to: dS = realmin(class(S)); while the new version of ISMEMBERF is submitted.
13 Oct 2009	Jan Simon	Beside the fact, that this is of practical use and works as expected, it helps to answer dozens of questions in the newsgroup: why does ANY((0:0.1:1) == 0.3) reply FALSE??? The help is complete and descriptive, contains author and date, exact and really useful comments. The H1-line is not helpful. Minor bug in line 125: if ndims(A) ~= 2 \|\| ndims(A) ~= 2. A simple [tf, loc] output might be more efficient than the VARARGOUT/Cell/DEAL/MIN/MAX/NARGOUT constructions.
13 Oct 2009	Carlos Adrian Vargas Aguilera	This is a nice function, thanks bruno for sharing it. You all may check out my NUMCMP function too. http://www.mathworks.com/matlabcentral/fileexchange/21190-numcmp-m Cheers, Carlos

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Updates
16 Mar 2009	Extend ISMEMBERF to complex arrays
19 Mar 2009	Important change in the engine when using 'rows' option, which saves the runtime by about 30%. Some adjustment with automatic tolerance.
10 Oct 2009	Correct bug reported by David
13 Oct 2009	Correct bug reported by Jan, better description in H1 line (thanks)

Tag Activity for this File
Tag	Applied By	Date/Time
ismember	Bruno Luong	16 Mar 2009 09:26:16
float	Bruno Luong	16 Mar 2009 09:26:16
round off	Bruno Luong	16 Mar 2009 09:26:16
numerical errors	Bruno Luong	16 Mar 2009 09:26:16

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