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I clicked on the Demonstration Project link, then browsed through the list of demos and decided to try the Monty Hall Problem demo.

It brings me to a flash application which lets me experiment with the problem by clicking on doors and then seeing where the prize is. Actually, it doesn't. It gives me two options: I can download a "live version", or I can watch a demo of someone else clicking on doors and seeing where the prize is. Hello? This is flash, it's already interactive! Gah..

Initial calculation - work out the lengths of each edge - the entire mesh forms a kite shaped prism.

(i) Calculate the numeric values of the vectors B->D, and A1->C, then calculate the dot product. That should equal zero.

Mostly I did it the way you've described but this first part was so easy I spend a lot of time trying to see a trivial solution for the other parts. (When I finally worked it all out and got arccos(sqrt(3)/sqrt(5)) for (iii) I decided that there perhaps wasn't a simple solution for (ii))

I was also somewhat confused by the wording. The only "square prism" I've ever come across is more commonly called a cuboid. http://mathworld.wolfram.com/SquarePrism.html agrees with me. Right prism is what they mean.

I also don't see the relevance of "foot of perpendicular is E" (but see my solution to (i) below)

For i:

Let E be the origin. Define a cartesian set of axes. ED define the X axis, EA the Y axis and the perpendicular to E the Z axis.

Now BD only has a component in the X axis while A1C only has components in the Y and Z axes therefore their dot product must be zero and thus BD and A1C must be perpendicular as they are both of non-zero length. QED.

Tim.

I don't think it's just about the spatial reasoning. The Chinese test questions are asking things that depend on a different definition of 'perpendicular' and 'angle', because the lines they are asking to prove perpendicular don't intersect, and the lines they are asking to find an angle between don't intersect either. As far as I know, definitions of perpendicular and angle require lines (or planes) to intersect. (so says Mathworld on angles and Mathworld on perpendicular, anyway)

So, unless the correct answers are "cannot be proven with Euclidean geometry" or to define a new geometry or new measure of angle, then this is a poorly translated test. (I can solve these easily if the questions were "prove the projections of the lines on each other such that they intersect are perpendicular" and "find the angle between the projection of the lines into the same plane.")

I don't think it's just about the spatial reasoning. The Chinese test questions are asking things that depend on a different definition of 'perpendicular' and 'angle', because the lines they are asking to prove perpendicular don't intersect, and the lines they are asking to find an angle between don't intersect either. As far as I know, definitions of perpendicular and angle require lines (or planes) to intersect. (so says Mathworld on angles and Mathworld on perpendicular, anyway)

So, unless the correct answers are "cannot be proven with Euclidean geometry" or to define a new geometry or new measure of angle, then this is a poorly translated test. (I can solve these easily if the questions were "prove the projections of the lines on each other such that they intersect are perpendicular" and "find the angle between the projection of the lines into the same plane.")

Hmm, what would be the energy requirements to create a "magnet bottle" to a distance of 20-30 kilometers?

Well, since the energy density of a magnetic field is (B^2)/(2*u0) (as given here), filling a sphere of radius 30km with 1 gauss (roughly the strength of the earth's field) would require 450 gigajoules. Of course, that's a really rough guess, and probably low, since the field would be a stronger as you get nearer the ship.

If you happen to have a time machine (which might look suspiciously like a DeLorean) handy, it would take 6.2 minutes to charge up the shields. :P

Slashdot editors should have listened in Physics class. This is the fourth time in 3 years, if I count correctly, that Slashdot editors have been fooled by the SAME scam.

See my previous comment, posted January 13, 2005: Distinguish between real science and junk science.

Planck's constant is so small that interactions between electromagnetic waves and molecules cannot be chemically specific. The 2,000 MHz radiation from cell phones is felt as heat, a very, very small amount of heat, almost certainly not measurable.

Anyone may have theories. Someone could say, for example, that pigs have started flying and they have been eating the bees. The only real science, however, is based on what is already known through experimentation. That requires an understanding of what is known.

The formula momentum=mass*velocity is a formula for the MECHANICAL momentum, which is just ONE kind of momentum. There are many kinds of momenta.

The best way to define momentum is through the concept of "generalized momentum". Every physical system is ultimately described by a quantity called a Lagrangian or Lagrangian density that's given to you axiomatically with respect to certain generalized coordinates. The generalized momentum is defined as the rate of change of the lagrangian with respect to the generalized velocity for a particular generalized coordinate. Notice that I have not put mass anywhere into the definition.

This means that anything that has a generalized coordinate, a corresponding generalized velocity and a lagrangian has a momentum, even massless objects. The relation p = m*v (non-relativistic) can be derived as a special case from the lagrangian of massive objects. In the case of light, which is massless, the generalized coordinate is the electromagnetic vector potential, and calculations on the postulated lagrangian show that the momentum is a product of the electric and Magnetic field called the Poynting Vector. You do second quantization on this and you get massless photons of the same momenta. Notice that mo mass was needed.

Sorry if the above sounds too pedantic. Somebody else may be able to offer a less technical explanation...

Refs:
http://en.wikipedia.org/wiki/Lagrangian
http://scienceworld.wolfram.com/physics/Generalize dMomentum.html
http://scienceworld.wolfram.com/physics/PoyntingVe ctor.html

The formula momentum=mass*velocity is a formula for the MECHANICAL momentum, which is just ONE kind of momentum. There are many kinds of momenta.

The best way to define momentum is through the concept of "generalized momentum". Every physical system is ultimately described by a quantity called a Lagrangian or Lagrangian density that's given to you axiomatically with respect to certain generalized coordinates. The generalized momentum is defined as the rate of change of the lagrangian with respect to the generalized velocity for a particular generalized coordinate. Notice that I have not put mass anywhere into the definition.

This means that anything that has a generalized coordinate, a corresponding generalized velocity and a lagrangian has a momentum, even massless objects. The relation p = m*v (non-relativistic) can be derived as a special case from the lagrangian of massive objects. In the case of light, which is massless, the generalized coordinate is the electromagnetic vector potential, and calculations on the postulated lagrangian show that the momentum is a product of the electric and Magnetic field called the Poynting Vector. You do second quantization on this and you get massless photons of the same momenta. Notice that mo mass was needed.

Sorry if the above sounds too pedantic. Somebody else may be able to offer a less technical explanation...

Refs:
http://en.wikipedia.org/wiki/Lagrangian
http://scienceworld.wolfram.com/physics/Generalize dMomentum.html
http://scienceworld.wolfram.com/physics/PoyntingVe ctor.html

A search on wiki gave these results http://en.wikipedia.org/wiki/Mock_theta_function http://en.wikipedia.org/wiki/Mock_theta_functions Both r informative,worth the read and ob not exhaustive...some external links given too. And the place where I find most of my info...WolframMathWorld ,the http://mathworld.wolfram.com/MockThetaFunction.htm llink directs to a page with some more info...

Arxiv doesn't appear to carry the paper, and only two papers in it relate to mock theta functions at all. One of them is a transformation formula for second-order mock theta functions and the other talks about mock theta functions as quantum invariants, whatever that means. A glance at the paper suggests that mock theta functions relate to a key element in topology, but my maths isn't nearly good enough to tell you exactly what is being described.

Arxiv doesn't appear to carry the paper, and only two papers in it relate to mock theta functions at all. One of them is a transformation formula for second-order mock theta functions and the other talks about mock theta functions as quantum invariants, whatever that means. A glance at the paper suggests that mock theta functions relate to a key element in topology, but my maths isn't nearly good enough to tell you exactly what is being described.

Arxiv doesn't appear to carry the paper, and only two papers in it relate to mock theta functions at all. One of them is a transformation formula for second-order mock theta functions and the other talks about mock theta functions as quantum invariants, whatever that means. A glance at the paper suggests that mock theta functions relate to a key element in topology, but my maths isn't nearly good enough to tell you exactly what is being described.

Arxiv doesn't appear to carry the paper, and only two papers in it relate to mock theta functions at all. One of them is a transformation formula for second-order mock theta functions and the other talks about mock theta functions as quantum invariants, whatever that means. A glance at the paper suggests that mock theta functions relate to a key element in topology, but my maths isn't nearly good enough to tell you exactly what is being described.

"I have discovered a truly marvelous demonstration of this proposition that this margin is too narrow to contain."

Engineer discovers that there are pros and cons in deciding between two systems, but has to make a general value judgment. The world does not obey trichotomy, you know.

I don't know. According to my calculations, the earth gets over 10^17 watts of solar energy. According to http://scienceworld.wolfram.com/physics/EnergyUsag e.html, people use slightly over 10^13 watts. So, we're increasing the earth's energy use by .007%, which doesn't seem too terrible to me.

Once you 'collapse' it (which I assume you have taken from the statement that observing a quantity collapses its wave function) future observations will all yield the same result. The probability function becomes zero for every value but the observed.

for instance, if the probability function was a gaussian distribution, You could think of "collapse" as reducing the width until it became a delta function.

Why not OSS for PalmOS: http://easycalc.sourceforge.net/
It has very advanced stuff, like erfc ( see http://mathworld.wolfram.com/Erfc.html )

A line is a straight one-dimensional figure having no thickness and extending infinitely in both directions. A line is sometimes called a straight line or, more archaically, a right line (Casey 1893), to emphasize that it has no "wiggles" anywhere along its length. While lines are intrinsically one-dimensional objects, they may be embedded in higher dimensional spaces.

Another great web page to put this discovery in context, with examples, citations, hotlinks, equations, tables, and the like:

Weisstein, Eric W. "Twin Primes." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/TwinPrimes.html

-- Prof. Jonathan Vos Post

Wow...

http://en.wikipedia.org/wiki/Billion

How about this for proof.

or this if you don't believe wikipedia:

http://www.jimloy.com/math/billion.htm

9 billion 1000 million (1 milliard)

9 zero's... 1,000,000,000

Or if you still don't believe me:

http://mathworld.wolfram.com/LargeNumber.html

Now, your turn find me just 1 site that says 1,000,000 is a billion.

Or are you just a troll?

Do you have any cites for this "common parlance" in which "rocking" does not involve movement? Or in which rotation doesn't involve movement? I don't know of anyone who would subscribe to this "common" parlance. They'd have to be pretty damn stupid to say that something which is rocking or rotating is not moving.

Well I guess I may be a little coloured by my exposure to mathematics, but none of my friends would refer to a rotating body as "moving", but they're mostly physicists and computer scientists, so therein may lie the problem in the difference between what I consider "common parlance" and what you consider "common parlance"...

So I'll offer up some references:

motion (m'shn)
n.

      1. The act or process of changing position or place.

"motion." The American Heritage® Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. 26 Dec. 2006.

While in mathematics rotation is defined as:

The turning of an object or coordinate system by an angle about a fixed point.

Weisstein, Eric W. "Rotation." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/Rotation.html

Which taking into account the previous definition of 'motion' means the object has not moved, as it's rotating around a fixed point.

That's just fucking retarded.

I guess that's one way to describe math. I imagine Pythagoras said something similar before he had Hipassus drowned for discovering irrational numbers. His shouting of epithets and subsequent termination (with extreme prejudice) of his student, however, did not change the truth behind Hipassus's proof. Extrapolate that experience onto our current one.

Motion does not just involve a displacement of the co-ordinates of the center-of-gravity of an object, it involves any part of it moving, or it moving about a rotational axis.

Well if I were to put a perfect sphere on the table in front of you, have you study it, hide it, rotate it, and then show it to you again and ask you if it had moved you'd be unable to give me an honest answer. However if I physically moved (noticed the word used) the sphere three inches to the left, you most likely would be able to tell me it was moved.

Also, I said nothing about a center of gravity. In the case of the Sixaxis its origin will most likely be at the point that lies closest to the center of where it is gripped by both hands, which may or may not be its center of gravity.

Once again, fucking retarded, as changes of orientation are - by definition - movement.

To loosely quote a favorite philosopher of mine, "Who's definition, joker? Yours or mine?"

How else does the videogame respond with movement when you change the rotation of the device?

I don't understand this question as phrased. Following my best attempt to understand, this is my answer: A programmer can map any input to any action in a game he or she so chooses. If somehow I could measure the rate of flatulence being expelled from a player I could easily map that to forward movement in a game. So mapping rotation to movement is not at all difficult. In face, Rayman Raving Rabbids does that in several minigames: mapping tilting the controller to moving a character on the screen.

As to what this soccer ball universe could floating in, well, the question itself is probably the largest issue. We don't know the answer, but the it could very well be that there is no "outside of the soccer ball". The universe could be all that there is. There could be no "beyond" the universe or "outside" of the universe. It is hard concept to visualize, but that is pretty much true of any concept that outside of the traditional Newtonian world.

One of the most confusing aspects of general relativity comes from the discussion of the expansion and curvature of the universe. To almost everyone, a curved surface can only be understood as such by treating it as being embedded in a higher dimensional space. But in reality, we don't have to think of it this way. Curvature is an intrinsic property of a manifold. That means that I can measure the curvature of the earth without ever leaving its surface or even walking all the way around. In fact, according to the gauss bonnet formula, all I need to do to measure the local curvature of the earth is measure (extremely precisely) the area of a triangle I draw on the ground. The field of differential geometry contains all the mathematical tools we need to describe the curvature of the universe, the metric (which lets us measure distances over curved surfaces) and it's evolution in time and space, and any other properties which you might think could only be understood if the universe was contained in something, but which actually make perfect mathematical sense if the universe is all that there is!

As to what this soccer ball universe could floating in, well, the question itself is probably the largest issue. We don't know the answer, but the it could very well be that there is no "outside of the soccer ball". The universe could be all that there is. There could be no "beyond" the universe or "outside" of the universe. It is hard concept to visualize, but that is pretty much true of any concept that outside of the traditional Newtonian world.

One of the most confusing aspects of general relativity comes from the discussion of the expansion and curvature of the universe. To almost everyone, a curved surface can only be understood as such by treating it as being embedded in a higher dimensional space. But in reality, we don't have to think of it this way. Curvature is an intrinsic property of a manifold. That means that I can measure the curvature of the earth without ever leaving its surface or even walking all the way around. In fact, according to the gauss bonnet formula, all I need to do to measure the local curvature of the earth is measure (extremely precisely) the area of a triangle I draw on the ground. The field of differential geometry contains all the mathematical tools we need to describe the curvature of the universe, the metric (which lets us measure distances over curved surfaces) and it's evolution in time and space, and any other properties which you might think could only be understood if the universe was contained in something, but which actually make perfect mathematical sense if the universe is all that there is!

Soccor Balls are not dodecahedra. They're truncated icosahedra.

l'Hopital's rule much? Just replace f and g with f' and g'... http://mathworld.wolfram.com/LHospitalsRule.html

t may come up in calculations and solutions but any physicist would be laugh out of the conference room if ever equated a measureable quantity to an number with imaginary component.

Awww, come on, there's nothing wrong with complex measures

http://mathworld.wolfram.com/ProjectivelyExtendedR ealNumbers.html
http://en.wikipedia.org/wiki/Real_projective_line

Division is defined in math by multiplication. a/b = x is defined as b*x = a.

You, sir, are incorrect. i is defined as sqrt(-1). See any algebra text or Mathworld for a reference.

How is this different from any other non-standard analysis approach?

Newton-Raphson is a method of repeatedly estimating the solution to an equation by refining guesses, using both the equation and its first derivative. This function does just a couple of steps. More information on NR can be found at Mathworld.

... conic section of water ...

But not a frust(r)um! Never that! Only the truly black-hearted minions of Nyarlathotep keep that filthy meme alive! Each utterance is an incantation that tears the dimensions asunder, forms claws of the very fabric of space and time and rips away an irreplaceable part of the memetic victim's mental integrity, delivering the scrap of soul to the master of insanity for his delectation and digestion.

Or something... It's just bad and wrong, mmm'kay?

You clearly didn't get the point of the DFT then, though that might not have been your fault. The DCT is nothing other than the DFT applied to even functions. Just about everything you need to know about DCTs you'll learn by studying DFTs. But DCTs are a restricted version of DFTs, DFTs are no harder than DCTs, and DFTs are incredibly useful in image processing (I've used them for fast convolution and image alignment via phase correlation), so just studying DCTs is plain stupid.

I see it another way: the Discrete Cosine Transform is a subclass, if you will, of a Discrete Fourier Transform. So it inherits properties of a DFT, and adds some properties of its own. The DFT then has certain properties by being a Fourier Transform, and by being a discrete transform. The discrete transform is then a special case of an integral transform. And so on. Hell, there is a whole branch of mathematics that studies things that are defined only as integral transforms.

Then you start looking at the concepts over mathemtical constructs other than real numbers. This is where things like error control coding (algebra with Galois Fields) and elliptic curve cryptography (algebra with elliptic curves) come from.

It all fits together. You can mix and match mathematical constructs and find out interesting things. And that generalization is, to me, what really matters.

...laura

(Some compositions I made.)

Obviously it depends on your field. I'm more involved with modeling than multimedia. However, my understanding was that professionals were using a forked version of gimp for video editing on linux clusters. Is there a commercial version that scales this far? I really don't know. But in terms of professional use, I don't think amateurs have clusters for their video editing.

Likewise, way back when Alias/Wavefront's Maya was cock-of-the-walk, it was available for Linux. Maya used to be *the* app for pro work. Graphics people seemed to be absolutely snobbish about it. Autodesk bought them from SGI, but it looks like Autodesk Maya 8 is still available for (64-bit only) linux. The hard core mathematical physics geek in me finds myself asking: have you looked at Mathematica for visual transformations? Sorry, had to ask...

I had friends who were into Bluegrass, and looking at recording their jam sessions (we are talking a couple hundred people showing up for three day weekends at least once per month thru the spring, summer, and into the fall). I didn't track their progress, as I graduated and moved on to another university, but the impression I gathered was that tools existed. I think they were using Ardour / Jack with RME Hammerfall cards. Obviously this won't work with SoundBlaster toys. Postings on a recent real time kernel article here at slashdot had a number of people talking about what acceptance of real time patches into the kernel will mean in terms of multi-channel live recording. I don't know if Jack is enough for "real" work, or if other real time patches are needed. Again, it isn't really my field. I do remember wanting to buy this really cool synthesizer, but couldn't rationalize it in my budget. $8,000 for a linux sound system? Thats alot of $$$ even for a Korg...

What made you sound like a troll was suggesting that the tens of thousands of applications that are available for linux aren't. If anything, the abundance of software is more disconcerting than the lack of it. If you want to know, "is MS Word available", well only using Wine or Crossover, which to my thinking means "no." If you want to know, "are there word processors", there are many many many approaches. I'm sorry if I misunderstood, I certainly didn't mean to be offensive.

So these aren't my fields, but hopefully this will point you towards information. My understanding is that for professional (studio labs) work, linux is there for audio and video, using Free tools. In terms of graphics, I won't debate gimp & blender & such, because I just don't know. Maya is supposed to be top of the line, though. Hope this helps :-)

Point. Let me clarify. Mathematically, they are the same thing. The principle of least action applies in both cases, just the path the minimizes the particular Lagrangian (T - V) (or Hamiltonian (T + V), if you prefer) differs depending on the potential energy. (Both methods are applications of the Calculus of Variations. ) Either way, it is a minimization problem and the same techniques apply. So, as far as I'm concerned, they tend to blend together.

Name me a problem and I can easily argue that it would be solvable (or not a problem at all) with 1/10th the population.

Ah, you must be one of those "mathematics denial" people. Here you go, from a trusted resource and using all the right symbols (which we can't on Slashdot) so you know it's the real deal. (Hint: look for the sentence that starts "We say A is a proper superset of B if..."

Maybe it would help if you actually saw a calendar. In England, September 15 1752 (2 days after the change) was a Friday. If you failed to take into account the calendar change then you'd expect that September 1 was also a Friday. But it wasn't. It was a Tuesday. So the calendar change changed which day of the month the Fridays fall on.

Your move. Fool.

It blew my mind to have pointed out to me (in John Derbyshire's EXCELLENT book Prime Obsession) that some infinite series sum to different values, depending upon the order in which the terms are added!

This amazing property is called "conditional convergence".

However, since we are dealing with only finite series in this instance, I think (hope) that we can assume that commutivity rules.

Technically, since Pi is infinitely long and never repeats, any finite series of digits must appear at some point.

Not necessarily. Determining whether pi is normal number - one that contains all digits with probability tending to 1/10, all 2-digit sequences with probability tending to 1/100, etc. has been quite difficult to the various number theorists who have looked at it.

"Never repeats" implies that you never repeat the entire string forever - not that substrings aren't repeated. It's obvious that 3.14159 1 14159 2 14159 3 14159 42 14159 1337 14 14159 8675309 etc. can be extended infinitely and still would never repeat. It's not so obvious that it contains every possible substring (and this result would directly depend on how you choose the numbers between the 14159s).

Technically, since Pi is infinitely long and never repeats, any finite series of digits must appear at some point.

Not necessarily. Determining whether pi is normal number - one that contains all digits with probability tending to 1/10, all 2-digit sequences with probability tending to 1/100, etc. has been quite difficult to the various number theorists who have looked at it.

"Never repeats" implies that you never repeat the entire string forever - not that substrings aren't repeated. It's obvious that 3.14159 1 14159 2 14159 3 14159 42 14159 1337 14 14159 8675309 etc. can be extended infinitely and still would never repeat. It's not so obvious that it contains every possible substring (and this result would directly depend on how you choose the numbers between the 14159s).

Given that few modern PCs even have ISA slots, the bang will often approach zero as well. Then you'd have to use l'Hopital's Rule to determine bang per buck.

It can only gain mass with speed if it has rest mass. Photons have zero rest mass. Zero times anything is zero.

Look up the Lorentz Transoform for how to calculate length contraction, mass increase and time dilation. Now try your baseball thrown at 100 miles an hour. You'll see that you have to be going at over half the speed of light to make any appreciable difference.

The momentum of the photon has nothing to do with mass.

See also "Special Relativity" by A P French, ISBN 0-412-34320-7, if it's still in print.

> -----Original Message-----
> From: James Heliotis [mailto:jeh@...]
>
> I have a student who is interested in doing a project adding
> design-by-contract assertions to another language. To my memory,
> I have never seen anything about how assertions are implemented in
> EiffelStudio, and what the challenges and pitfalls were. Can anyone
> point me to any documentation?
>
> Thanks a lot,
> James

Dear Jim:

Your student should find the following links useful:

http://www.phact.org/e/dennis4.html
http://mathworld.wolfram.com/CircleSquaring.html
http://chemistry.about.com/cs/generalchemistry/a/a a050601a.htm

Hope this helps,

-- Bertrand Meyer

http://tech.groups.yahoo.com/group/eiffel_software /message/3558

Mersenne primes are simply primes that have this form, but not all numbers that have this form are prime. For example, 15 = 2^4 -1 and is not prime.

Also, for a number to be a Mersenne prime, the 'n' from 2^n-1 must be prime (according to Mathworld).

I would just like to say in my defense that in the form I submitted the story it wasn't just a shameless plug for my poster. It was a shameful plug disguised with interesting links to the recent Brainiac alkali metal explosions fiasco, which I'm genuinely surprised didn't get any attention on slashdot. Sorry about the server, again. It was supposed to be able to handle it. Unfortunately they have their hands around my bandwidth neck because for some reason our sysadmin department feels it's more important to keep wolfram.com running than my periodic table table site. Where is the appreciation for fine art in this world? If only people would buy my poster, I could afford more bandwidth for sodium explosions. There, now you have a truly shameless plug to complain about.

So... how about snakes on a hyperplane http://mathworld.wolfram.com/Hyperplane.html?

these weird tests that you think can peer into the heart of any programmer

I'm not (much) interested in peering into the heart of a programmer, but into their mind. And it doesn't have much to do with whether they can generate correct code or not; generating correct code is so easy that even a computer program can do it. It has a lot to do with how adaptable the programmer is -- is this guy going to be any good two years from now when the technology has changed? (Granted, interviewing style is going to be different if you're just looking for someone for a 3-month project vs a permanent long term hire.)

Programming is kind of weird in that something can outwardly function, but yet be terribly coded. I don't know of many other fields where this is true.

Geez, look at the internals of almost any consumer device, or look at a house under construction, or... etc. It's true of almost anything where the manufacturer/builder can wrap a pretty skin around it that will hold up for a minimal amount of time. That's why there are things like electrical codes and building codes and inspectors. Software isn't quite there yet, except in certain critical fields like avionics. If commercial software had to have something equivalent to a UL certification, the whole field would collapse overnight.

Most people looking for "voodoo indicators" are probably techies who don't really have a clue how they themselves do what they do, so they don't know how to look for it in other people. (Having miserable people-skills in the first place may have something to do with that, too.)

On the other hand what you may think is a voodoo indicator may actually be something that is important to the project/company and extremely relevant in the interviewer's experience, or that they're using that to find out something other than what you think they are.

An example: one of my fellow senior programmers/technical interviewers at a company where the work involved a lot of computational geometry was fond of asking about finding convex hulls. Unlikely that anyone could give a good technical answer off the cuff unless they'd just completed a course on it or had worked in that field for a while -- and even then there's no single right answer. That wasn't the point; the point was to see how the candidate reacted to the question. Being ignorant was okay so long as they were honest (extra points for coming up with some intelligent suggestions for finding out the answer) -- we had a database team, a UI team, etc where that kind of mathematical knowledge wasn't as important. But trying to bullshit your way through an answer was fatal. If you started talking about boats, you might be shown the door right then ;-)

A candidate might view that question about computing a convex hull as a voodoo indicator, especially if they didn't know the answer and they didn't get a job offer. But they might have blown the interview for totally unrelated reasons -- as might well have somebody who could discourse at length on the relative merits of various convex hull algorithms.