Doug’s MATLAB Video Tutorials

November 6th, 2009

I like his slow, clear, methodical presentation with great visualizations. It is the first time I have deeply understood some of the volume visualization techniques we have.

• 1 of 9 Definitions for scalar and vector fields.
• 2 of 9 Examples of scalar and vector fields (temperature in a room vs air currents)
• 3 of 9 Displays scatter3 and slice plots.

15:05 UTC | Posted in Format: Video, Level: Basic | Permalink | 1 Comment »

November 4th, 2009

Get all the information here.

Our more faithful blog readers might have a head start on this puzzle…

Finding four connected regions.

A puzzler about the game that inspired this contest.

Winning entries to the above puzzler.

17:05 UTC | Posted in Topic: Puzzler | Permalink | No Comments »

November 3rd, 2009

“For two coins (i.e. Frisbees®) that have the same probability of being heads or tails (but not necessarily fair coins) you are at worst going to win 50% of the time when you choose ’same’.” (Here is the original post)

My argument on the Ultimate Frisbee field was

“Imagine the two Frisbee come up heads 99% of the time, what do you choose?”

“Same!”

“What about 98%?”

“Same”

“This logic holds all the way through, even to 50.00001. At 50% it just does not matter, so always choose same.”

The more rigorous and MATLAB proofs were more along these lines:

This was a GUI that you watched as it went through a Monte Carlo simulation. Thanks Richard

Arman did a more traditional proof, citing Wikipedia

Let p be the probability of having tails.
The probability of having "different" is p(1-p)+(1-p)p.
The probability of having "same" is p^2+(1-p)^2.

From the arithmetic mean geometric mean inequality, we know that

p^2+(1-p)^2 >= 2*p(1-p) and equality holds if p=1-p which means p=1/2.

Therefore “same” is better choice for any p value.

There were many variations on this plot:

I liked Zane’s here because it shows how much better off you are with ’same’ for each value of unfairness in the coin.

Christopher won the challenge by going to the next level, pointing out that you could make these unfair Frisbees almost fair by flipping three and calling for an odd number (1 or 3) vs even number (0 or 2) of heads.

Thank you everyone for playing, and finally putting this question to rest! Now the ethical question, knowing the coin flip is unfair, is it in the Spirit of The Game to let the other guy choose? Should we move to Christopher’s method of flipping three Frisbees?

Frisbee® is a Registered Trademark of © 2004 Wham-o Inc. All Rights Reserved.

14:49 UTC | Posted in Level: Basic, Topic: Puzzler | Permalink | 2 Comments »

October 30th, 2009

I like his slow, clear, methodical presentation with great visualizations. It is the first time I have deeply understood some of the volume visualization techniques we have.

• 1 of 9 Definitions for scalar and vector fields.
• 2 of 9 Examples of scalar and vector fields (temperature in a room vs air currents)

20:44 UTC | Posted in Format: Video, Level: Basic | Permalink | 2 Comments »

October 27th, 2009

I made a convincing argument, but I am curious what kind of persuasive MATLAB-based ‘proofs’ can be made. I am offering a MATLAB t-shirt to the most persuasive entry. Use published MATLAB files, GUI’s, MATLAB script or function, whatever you think will be most convincing. Contest ends this time next week.

Assumptions: The Frisbees (or coins) are either ‘heads’ or ‘tails’. The coins may or may not be ‘fair’ (i.e. they might be heads 80% of the time!), however the odds of heads versus tails for the two coins is the same for both coins. Send entries to hull@MathWorks.com (no .rar files please!) (Here is the result of this now closed contest)

Frisbee® is a Registered Trademark of © 2004 Wham-o Inc. All Rights Reserved.

19:31 UTC | Posted in Level: Basic, Topic: Puzzler | Permalink | 3 Comments »

October 23rd, 2009

I like his slow, clear, methodical presentation with great visualizations. It is the first time I have deeply understood some of the volume visualization techniques we have. Sorry, Dr. H, but I really did not understand Div, Grad, Curl and all of that until Patrick explained it later in this series!

1 of 9 Definitions for scalar and vector fields.

15:26 UTC | Posted in Level: Basic | Permalink | 5 Comments »

October 14th, 2009

Come hear Keynote speakers starting at 7:45 EST.

See the rest of the schedule

I have four new puzzler listed, when you arrive come stop by the booth, grab a copy and try to solve them to get some MATLAB gifts.

11:16 UTC | Posted in Topic: Puzzler | Permalink | No Comments »

October 9th, 2009

 x1 = rand(1,10);
 y1 = rand(1,10);

 vi = convhull(x1,y1);
 polyarea(x1(vi),y1(vi))

 plot(x1,y1,'.')
 axis equal
 hold on
 fill ( x1(vi), y1(vi), 'r','facealpha', 0.5 ); 
 hold off

13:30 UTC | Posted in Format: Video, Level: Basic | Permalink | No Comments »

October 2nd, 2009

sales.rep    = [1 2 1 3 4 6 2 3 1 1];
sales.amount = [1 1 3 1 5 2 2 4 1 5];


numReps = max(sales.rep);
sales.total   = zeros(1,numReps);
for i = 1 : numel(sales.rep)
    sales.total(sales.rep(i)) = sales.total(sales.rep(i)) ...
                              + sales.amount(i);
end


sales.accum = accumarray(sales.rep', sales.amount)'

14:37 UTC | Posted in Level: Basic | Permalink | No Comments »

September 25th, 2009

I have been asked to write a few Puzzlers to be posed at my booth. There are a couple of good ones written already, with more to come. It is a lot of fun to think that when I was a kid I read Games magazine and thought how cool it would be to make puzzles for a job… Now it is one of the duties that I take on here at The MathWorks from time to time!

Please sign up for the virtual conference and stop in to say hello.

20:42 UTC | Posted in Topic: Puzzler | Permalink | No Comments »

These postings are the author's and don't necessarily represent the opinions of The MathWorks.