I wanted to evaluate the performance of the matlab routines fftfilt()
and conv() (freq/time domain filtering), so I wrote a little m file to
compare the processing load in flops and elapsed time using tic/toc.
The results, for a 100k-sample input with 128 filter coefficients,
FFT: time 5.310000e-001, flops 1.123790e+007
conv: time 4.400000e-001, flops 2.560002e+007, ratio fft/conv
I'm curious why the fftfilt() routine took longer to run, yet had only
44% of the conv() flops. Any ideas?
Remove first character from domain name to reply.
Subject:fftfilt() vs conv() timings From:Thomas P. Krauss Date: 24 Jun, 1998 13:34:12 Message: 2 of 2
James Nichols wrote:
> I wanted to evaluate the performance of the matlab routines fftfilt()
> and conv() (freq/time domain filtering), so I wrote a little m file to
> compare the processing load in flops and elapsed time using tic/toc.
> The results, for a 100k-sample input with 128 filter coefficients,
> FFT: time 5.310000e-001, flops 1.123790e+007
> conv: time 4.400000e-001, flops 2.560002e+007, ratio fft/conv
> I'm curious why the fftfilt() routine took longer to run, yet had only
> 44% of the conv() flops. Any ideas?
Many operations that MATLAB performs do not register as FLOPS,
for example, creating and copying matrices. The main reason fftfilt
takes longer is that it has a while loop and is an M-file, while
conv is built-in. Note for FIR filtering, upfirdn (a MEX-file)
runs about twice as fast as conv.
A quick timing experiment on my Mac indicates that the filter and
signal length have to be REALLY long before fftfilt saves you
a lot of time:
Playing with the block size parameter sometimes can increase
the speed... the heuristic that fftfilt uses to choose the
block length is based on fft flops and the number of blocks,
and it doesn't always yield the fastest time.
Note that fftfilt could be rewritten to take more than 1 FFT
at a time, to reduce the amount of looping required (ala
medfilt1). This would use a lot more memory, but execute
*much* faster. Are you listening, MathWorks? (geck, geck, geck...)
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.
How do I add an item to my watch list?
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.
Tags for this Thread
No tags are associated with this thread.
What are tags?
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.
About Newsgroups, Newsreaders, and MATLAB Central
What are newsgroups?
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.
How do I read or post to the newsgroups?
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.
Other ways to access the newsgroups
Use a newsreader through your school, employer, or internet service provider
Pay for newsgroup access from a commercial provider
Use Google Groups
Mathforum.org provides a newsreader with access to the comp.soft sys.matlab newsgroup