Got this peculiar problem that sum (and also prod) appears to depend on the order of the values in the array that is supposed to be summed up.
Consider this code:
load tmptmp1 % loads only the array, nothing else.
% indeces 1:
ii1=[ 21 29 27 25 22 38 23 28 35 1];
% indeces 2, the 3rd and last index changed positions
ii2=[ 21 29 1 25 22 38 23 28 35 27];
% read out the values from the array using the indeces:
% make sure, all val1 values appear also in val2:
% although val1 and val2 have exactly the same values, their sum is different:
% not so, if val1 and val2 are sorted first:
1 1 1 1 1 1 1 1 1 1
Any ideas what's going on? I use the following Matlab version
MATLAB Version 18.104.22.1689 (R2010a)
MATLAB License Number: STUDENT
Operating System: Microsoft Windows Vista Version 6.0 (Build 6002: Service Pack 2)
Java VM Version: Java 1.6.0_12-b04 with Sun Microsystems Inc. Java HotSpot(TM) Client VM mixed mode
MATLAB Version 7.10 (R2010a)
Simulink Version 7.5 (R2010a)
Bioinformatics Toolbox Version 3.5 (R2010a)
Control System Toolbox Version 8.5 (R2010a)
Curve Fitting Toolbox Version 2.2 (R2010a)
EzyFit Toolbox Version 2.30
Global Optimization Toolbox Version 3.0 (R2010a)
Image Processing Toolbox Version 7.0 (R2010a)
MATLAB Report Generator Version 3.8 (R2010a)
Optimization Toolbox Version 5.0 (R2010a)
Partial Differential Equation Toolbox Version 1.0.16 (R2010a)
Signal Processing Blockset Version 7.0 (R2010a)
Signal Processing Toolbox Version 6.13 (R2010a)
Spreadsheet Link EX Version 3.1.1 (R2010a)
Statistics Toolbox Version 7.3 (R2010a)
Symbolic Math Toolbox Version 5.4 (R2010a)
Thanks a bunch!
PS: here is the content of the array:
"David" wrote in message <email@example.com>...
> Got this peculiar problem that sum (and also prod) appears to depend on the order of the values in the array that is supposed to be summed up. .......
- - - - - - - - - - -
You have no reason to suppose that in any computer's calculation of numbers where round off errors can occur, these will automatically give exactly the same net result for different orderings of operations. All you can expect is that each such error is within the range expected of such errors. This is a characteristic of all digital computing, not just matlab.
You can think of your watch list as threads that you have bookmarked.
You can add tags, authors, threads, and even search results to your watch list. This way you can easily keep track of topics that you're interested in. To view your watch list, click on the "My Newsreader" link.
To add items to your watch list, click the "add to watch list" link at the bottom of any page.
To add search criteria to your watch list, search for the desired term in the search box. Click on the "Add this search to my watch list" link on the search results page.
You can also add a tag to your watch list by searching for the tag with the directive "tag:tag_name" where tag_name is the name of the tag you would like to watch.
To add an author to your watch list, go to the author's profile page and click on the "Add this author to my watch list" link at the top of the page. You can also add an author to your watch list by going to a thread that the author has posted to and clicking on the "Add this author to my watch list" link. You will be notified whenever the author makes a post.
To add a thread to your watch list, go to the thread page and click the "Add this thread to my watch list" link at the top of the page.
A tag is like a keyword or category label associated with each thread. Tags make it easier for you to find threads of interest.
Anyone can tag a thread. Tags are public and visible to everyone.
The newsgroups are a worldwide forum that is open to everyone. Newsgroups are used to discuss a huge range of topics, make announcements, and trade files.
Discussions are threaded, or grouped in a way that allows you to read a posted message and all of its replies in chronological order. This makes it easy to follow the thread of the conversation, and to see what’s already been said before you post your own reply or make a new posting.
Newsgroup content is distributed by servers hosted by various organizations on the Internet. Messages are exchanged and managed using open-standard protocols. No single entity “owns” the newsgroups.
There are thousands of newsgroups, each addressing a single topic or area of interest. The MATLAB Central Newsreader posts and displays messages in the comp.soft-sys.matlab newsgroup.
You can use the integrated newsreader at the MATLAB Central website to read and post messages in this newsgroup. MATLAB Central is hosted by MathWorks.
Messages posted through the MATLAB Central Newsreader are seen by everyone using the newsgroups, regardless of how they access the newsgroups. There are several advantages to using MATLAB Central.
Your MATLAB Central account is tied to your MathWorks Account for easy access.
Use the Email Address of Your Choice
The MATLAB Central Newsreader allows you to define an alternative email address as your posting address, avoiding clutter in your primary mailbox and reducing spam.
Most newsgroup spam is filtered out by the MATLAB Central Newsreader.
Messages can be tagged with a relevant label by any signed-in user. Tags can be used as keywords to find particular files of interest, or as a way to categorize your bookmarked postings. You may choose to allow others to view your tags, and you can view or search others’ tags as well as those of the community at large. Tagging provides a way to see both the big trends and the smaller, more obscure ideas and applications.
Setting up watch lists allows you to be notified of updates made to postings selected by author, thread, or any search variable. Your watch list notifications can be sent by email (daily digest or immediate), displayed in My Newsreader, or sent via RSS feed.