Rank: 847 based on 128 downloads (last 30 days) and 7 files submitted

Zhigang Xu

E-mail: xuz@dfo-mpo.gc.ca
Company/University: Bedford Inst of Oceanography

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Files

Files Posted by Zhigang				View all 1 - 5 of 7
Updated	File	Tags	Downloads (last 30 days)	Comments	Rating
05 Sep 2009	NUMUNIQUE Returns unique elements in an array and all the indices for the repetitious values. Author: Zhigang Xu	sort, set, numunique, unique, mathematics	21	10	5.0 5.0 \| 2 ratings
28 Aug 2009	tidal_ellipse Consists of two tidal ellipse conversion programs Author: Zhigang Xu	conversion, tidal ellipse, earth sciences, tools	21	1	4.0 4.0 \| 1 rating
28 Aug 2009	Converts between decimal integers to multiple based numbers Converts between decimal integers to multiple based numbers. Author: Zhigang Xu	vectorization, data structure, computer science, binary tree search, mathematics	18	0
07 Jul 2008	Zero Out Smalls To zero out the small elements whose absolute values are smaller than a given criterion. Author: Zhigang Xu	small quantities, eps, zeros	9	4
07 Jul 2008	ATAN2_SAFE To perform the same function as Matlab built-in function atan2 but safely guarded against erroneous Author: Zhigang Xu	erroneous small input..., safe, inputs, builtin, mathematics, atan2	15	6	1.0 1.0 \| 2 ratings

Comments and Ratings by Zhigang		View all 1 - 5 of 7
Updated	File	Comments	Rating
06 Sep 2009	ATAN2_SAFE To perform the same function as Matlab built-in function atan2 but safely guarded against erroneous Author: Zhigang Xu	ATAN2 is fine if you can be watchful each time for its small inputs, whereas, as has been said above, "To relieve you from the cleaning burden every time when you need to call ATAN2, ATAN2_safe automates the cleaning and the calling two steps for you."
05 Sep 2009	NUMUNIQUE Returns unique elements in an array and all the indices for the repetitious values. Author: Zhigang Xu	Ah, the explanation to the above puzzle (i.e., NaN vs Double) lies in that whenever NaN is concatenated with other classes, it will be converted to zero first. Thus, uint8(nan) ans = 0 int32(nan) ans = 0 [nan uint16([1 2])] ans = 0 1 2 whereas [nan double([1 2])] ans = NaN 1 2 A lesson to remember is that NaN is only a not-a-number within double class. It will become zero when it is converted to other classes.
05 Sep 2009	NUMUNIQUE Returns unique elements in an array and all the indices for the repetitious values. Author: Zhigang Xu	This is a very thoughtful suggestion. Thanks! I did a quick experiment as follows, showing that NaN can only work with a double class to get right logical indices. I will implement your suggestion for next updating. Thanks again! >> diff([nan [0 1]])~=0 ans = 1 1 >> diff([nan uint8([0 1])])~=0 ans = 0 1
04 Sep 2009	NUMUNIQUE Returns unique elements in an array and all the indices for the repetitious values. Author: Zhigang Xu	Matt, Thanks for your comments and rating. Your suggestion can evidently make the codes more concise. However, using logical indexing is usually faster than FIND, as the Matlab Editor would advise. For this reason, I am hesitating to implement it for now. I tested your suggestion with a large input array (x=randi(999, 7e6,1)), and did not find any significant improvement in speed, although it did not go slower either. I am wondering if you can supply me your test script to show the significant difference in speed. I will be very happy to implement your suggestion after I understand why it can do so. Thanks! Zhigang
04 Sep 2009	NUMUNIQUE Returns unique elements in an array and all the indices for the repetitious values. Author: Zhigang Xu	The updated version has been just up now (as 04-Sep-2009 11:09:21). So please feel free to download the new version. Thanks! --- Zhigang

Comments and Ratings on Zhigang's Files			View all 1 - 5 of 23
Updated	File	Comment by	Comments	Rating
06 Sep 2009	ATAN2_SAFE To perform the same function as Matlab built-in function atan2 but safely guarded against erroneous Author: Zhigang Xu	Xu, Zhigang	ATAN2 is fine if you can be watchful each time for its small inputs, whereas, as has been said above, "To relieve you from the cleaning burden every time when you need to call ATAN2, ATAN2_safe automates the cleaning and the calling two steps for you."
05 Sep 2009	NUMUNIQUE Returns unique elements in an array and all the indices for the repetitious values. Author: Zhigang Xu	Xu, Zhigang	Ah, the explanation to the above puzzle (i.e., NaN vs Double) lies in that whenever NaN is concatenated with other classes, it will be converted to zero first. Thus, uint8(nan) ans = 0 int32(nan) ans = 0 [nan uint16([1 2])] ans = 0 1 2 whereas [nan double([1 2])] ans = NaN 1 2 A lesson to remember is that NaN is only a not-a-number within double class. It will become zero when it is converted to other classes.
05 Sep 2009	NUMUNIQUE Returns unique elements in an array and all the indices for the repetitious values. Author: Zhigang Xu	Xu, Zhigang	This is a very thoughtful suggestion. Thanks! I did a quick experiment as follows, showing that NaN can only work with a double class to get right logical indices. I will implement your suggestion for next updating. Thanks again! >> diff([nan [0 1]])~=0 ans = 1 1 >> diff([nan uint8([0 1])])~=0 ans = 0 1
05 Sep 2009	NUMUNIQUE Returns unique elements in an array and all the indices for the repetitious values. Author: Zhigang Xu	Luong, Bruno	To make the function work for other integer class, I would suggest to modify the two lines: d=diff([NaN; x]); d=[true; d~=0]; to: d=diff(x); d=[true; d~=0]; Otherwise unexpected result is obtained with [u p]=numunique(uint8([0 1]))
04 Sep 2009	NUMUNIQUE Returns unique elements in an array and all the indices for the repetitious values. Author: Zhigang Xu	Xu, Zhigang	Matt, Thanks for your comments and rating. Your suggestion can evidently make the codes more concise. However, using logical indexing is usually faster than FIND, as the Matlab Editor would advise. For this reason, I am hesitating to implement it for now. I tested your suggestion with a large input array (x=randi(999, 7e6,1)), and did not find any significant improvement in speed, although it did not go slower either. I am wondering if you can supply me your test script to show the significant difference in speed. I will be very happy to implement your suggestion after I understand why it can do so. Thanks! Zhigang

Top Tags Applied by Zhigang	1 - 5 of 32
mathematics, earth sciences, atan2, binary tree search, builtin

Files Tagged by Zhigang				View all 1 - 5 of 8
Updated	File	Tags	Downloads (last 30 days)	Comments	Rating
05 Sep 2009	NUMUNIQUE Returns unique elements in an array and all the indices for the repetitious values. Author: Zhigang Xu	sort, set, numunique, unique, mathematics	21	10	5.0 5.0 \| 2 ratings
28 Aug 2009	tidal_ellipse Consists of two tidal ellipse conversion programs Author: Zhigang Xu	conversion, tidal ellipse, earth sciences, tools	21	1	4.0 4.0 \| 1 rating
28 Aug 2009	Converts between decimal integers to multiple based numbers Converts between decimal integers to multiple based numbers. Author: Zhigang Xu	vectorization, data structure, computer science, binary tree search, mathematics	18	0
17 Mar 2009	SC - powerful image rendering Useful tool for rendering and outputting information rich images Author: Oliver Woodford	colormap, color, render, image, greyscale, nans	276	15	4.83333 4.8 \| 12 ratings
07 Jul 2008	Zero Out Smalls To zero out the small elements whose absolute values are smaller than a given criterion. Author: Zhigang Xu	small quantities, eps, zeros	9	4

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