## Search found 74 matches

Thu Apr 19, 2012 1:57 am UTC
Forum: Mathematics
Topic: Help identifying image noise
Replies: 13
Views: 2022

### Re: Help identifying image noise

Well I ended up thinking long and hard about A2 and getting something like A3. Here's the little snippet of Python code that I wrote: def objective(image): dim=shape(image) measure=0 for i in xrange(1,dim[0]): for ii in xrange(1,dim[1]): measure+=(image[i,ii]*image[i-1,ii-1]+image[i-1,ii]*image[i,ii...
Wed Apr 18, 2012 12:35 pm UTC
Forum: Mathematics
Topic: Help identifying image noise
Replies: 13
Views: 2022

### Re: Help identifying image noise

Can I just ask, do you have any more info on what the "optimizer" you refer to in the original post doing? Can it give you probabilistic data of star location, numbers, etc, or is it essentially a black box that spits out a list of 'stars found here, here and here'? See, as you've explain...
Wed Apr 18, 2012 5:07 am UTC
Forum: Mathematics
Topic: Help identifying image noise
Replies: 13
Views: 2022

### Re: Help identifying image noise

I am just picking out the stars and giving that information back to my astrophysics friend. I am not dealing with any calibration or hardware, so I assume that this data has been properly conditioned to remove all of the noise that is easily removable. In fact most of the data I am dealing with righ...
Wed Apr 18, 2012 1:31 am UTC
Forum: Mathematics
Topic: Help identifying image noise
Replies: 13
Views: 2022

### Re: Help identifying image noise

Hmmm, that seems kind of vague, especially considering it might be a single smudge in a noisy field, not necessarily whole image blurring, the correlation over the whole image might be very small. I'll work on it though. One of the other approaches I was thinking of was some sort of entropy measure....
Tue Apr 17, 2012 9:48 pm UTC
Forum: Logic Puzzles
Topic: Counting quarters blindfolded
Replies: 2
Views: 3084

### Counting quarters blindfolded

I searched and couldn't find this one: You are kidnapped and put in a chair with a bag over your head, so you can't see anything. In front of you is a table covered in 300 quarters. You have one hour to separate the quarters into two piles. Each pile must have an equal number of heads-up quarters. I...
Tue Apr 17, 2012 8:02 pm UTC
Forum: Mathematics
Topic: Help identifying image noise
Replies: 13
Views: 2022

### Re: Help identifying image noise

Okay, so what measurement would you recommend distilling from the autocorrelation image? A mean value cutoff threshold maybe?
Tue Apr 17, 2012 3:33 am UTC
Forum: Logic Puzzles
Topic: 17 Offices
Replies: 19
Views: 4162

### Re: 17 Offices

If Albert and Brenda share information, how soon can they expect to find their professor? Give answer in number of hours, plus give your algorithm. Expected value is different from maximum value. All of these algorithms are minimizing the maximum number of checks, not minimizing the expected number...
Tue Apr 17, 2012 3:22 am UTC
Forum: Mathematics
Topic: Help identifying image noise
Replies: 13
Views: 2022

### Re: Help identifying image noise

Well I imagine I don't need to autocorrelate the whole image, just neighbouring pixels. Maybe I could do a moving 5x5 autocorrelation for each pixel. But what specific value could I use as a measure for the whole image? Should I look for any average correlation value above a threshold?
Mon Apr 16, 2012 11:46 pm UTC
Forum: Mathematics
Topic: Help identifying image noise
Replies: 13
Views: 2022

### Help identifying image noise

I am a bit out of my field here, so please excuse me if I use the wrong terminology or don't know obvious theory. This is part of a problem I am working on to implement optimization algorithms on automated star detection for sky surveys. Specifically for dim, clustered stars in noisy fields. That is...
Mon Mar 26, 2012 3:29 pm UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

Which definition do you think changes with every observation? Sure, that is what the observable universe does, but is that surprising? It's right there in the name. The advantage of the conventional nomenclature is that we can distinguish between the observable universe and the universe as a whole....
Mon Mar 26, 2012 9:52 am UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

Good job on completely and totally missing the point of my example. No, an object on the opposite side of the ring outside your horizon cannot affect you, but what you cannot do is pick an object, define the horizon around it to be a universe, and then declare that nothing in this universe can ever...
Mon Mar 26, 2012 8:26 am UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

So your definition of the universe depends on the laws of physics within that universe. In your universe, If something flies off beyond any possible interaction and has no further effect whatsoever on anything else within the universe, it continues to exist, but if it were to magically disappear and...
Mon Mar 26, 2012 3:31 am UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

Except, we can see things which are moving away faster than light. Because it's space that's expanding, rather than anything moving through space. No we aren't getting light from any object moving faster than light. Consider what the wavelength would be. And it is useless because what is part of it...
Mon Mar 26, 2012 1:38 am UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

No, a galaxy really truly could recede outside of our light cone, if expansion is accelerating as it seems to be. It is most definitely *not* physically impossible. The difference is that, according to real physics, "the universe" still includes that galaxy, even if the observable univers...
Sun Mar 25, 2012 11:52 pm UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

You guys are all thinking of time as some fixed absolute. You are trying to fit the universe into an objective reference frame of knowledge while still keeping all of the relative aspects of time and space. Time is relative to the observer. If you want to consider a reference throughout all of time ...
Sun Mar 25, 2012 10:03 pm UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

I don't think anyone suggested that far away things don't exist. I said that things with no effect on us (direct or indirect) don't exist. It defines things in a relative manner rather than an absolute manner, and I think it is clear that existence is relative. If you existed in an alternate reality...
Sun Mar 25, 2012 8:20 pm UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

So you're positing a huge violation of mass/energy conservation, whereby entire galaxies can cease to exist. Also, what about an object in between that can still observe both our galaxy and the distant one? It's a strange definition of "universe" that is intransitive. We are in the same u...
Fri Mar 23, 2012 8:54 pm UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

And if the early inflation of the universe happened fast enough, then there are absolutely things that didn't interact with us at that time, but which could eventually enter our light cone in the future, if the relative motion and expansion rate happen to be right for that. Also, what about things ...
Fri Mar 23, 2012 5:26 pm UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

If the galaxy is "outside of the universe" at the beginning there, so is everything other than the particle whose reference frame we're in. By that and your definition that nothing exists outside the universe, there should be a single particle in the universe. That whose frame we're in. T...
Fri Mar 23, 2012 2:28 am UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

Here's the diagram I promised. This shows that it is possible for an object whose worldline was entirely outside an observer's past lightcone at one point in time can have some (or all) of its worldline contained within the observer's past lightcone (it can enter the observer's lightcone) given a b...
Tue Mar 20, 2012 11:22 pm UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

What you've just described is an event occurring at that galaxy entering the light cone. The past galaxy of course already interacted with us. The galaxy exists and existed previously, from the reference frame of r=0 t=0, the event you have described as occurring at t=0 and r=galaxy does not yet exi...
Tue Mar 20, 2012 10:21 pm UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

But now your definition of the word universe has no common use, or logical basis. Your definition of the universe includes everything existent, and non-existent. At least my definition is tied to the reality we inhabit and generally accepted by most people I've spoken with. As far as I am concerned...
Tue Mar 20, 2012 10:09 pm UTC
Forum: Science
Topic: Why do airplanes need wings?
Replies: 66
Views: 9781

### Re: Why do airplanes need wings?

I stand corrected on supersonic planes. But I still stand by the fact that if you are accelerating air to achieve lift, the greater the mass of air you accelerate, the less power you need. That's totally counterintuitive. That's like saying, "the heavier the wheelbarrow you have, the less forc...
Tue Mar 20, 2012 8:06 pm UTC
Forum: Science
Topic: Why do airplanes need wings?
Replies: 66
Views: 9781

### Re: Why do airplanes need wings?

There are only (basically) two sources of drag: Induced drag and parasite drag. The induced drag is typically a small component of the overall drag, and is a much smaller component on a supersonic jet than a non-supersonic jet. Even if an airplane is "falling", it's still producing enormo...
Tue Mar 20, 2012 7:33 pm UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

Sorry, you just play around with words here. You can call the MWI "one-world-interpretation" and consider all elements of its world-view as part of a single universe/world (which is one thing I personally prefer btw.), and your argument is gone. But now your definition of the word univers...
Tue Mar 20, 2012 5:35 pm UTC
Forum: Science
Topic: Nondeterministic Universe, posible?
Replies: 70
Views: 8329

### Re: Nondeterministic Universe, posible?

Multiworld theory isn't really a theory at all: To say that we will randomly be in a universe which is one of a set of many universes where every possibility has occurred, is EXACTLY the same thing as saying that the result is some random function. You're either randomly placed in one of many univer...
Tue Mar 20, 2012 4:00 pm UTC
Forum: Science
Topic: Why do airplanes need wings?
Replies: 66
Views: 9781

### Re: Why do airplanes need wings?

The larger the mass flow rate you are accelerating downwards, the less power you need to stay in the air. That's really actually the opposite of what is true. How so? I think we have all agreed that heavier than air flight ultimately requires the acceleration of air downwards for the plane to stay ...
Fri Mar 16, 2012 7:56 pm UTC
Forum: Science
Topic: Why do airplanes need wings?
Replies: 66
Views: 9781

### Re: Why do airplanes need wings?

I think you kind of missed my point in the last post. The original question was why do planes need wings instead of just pointing their engines downwards, because in the end you're just staying up there by accelerating air downwards. It came up that for a prop driven plane at least, this is basicall...
Fri Mar 16, 2012 5:21 pm UTC
Forum: Science
Topic: Why do airplanes need wings?
Replies: 66
Views: 9781

### Re: Why do airplanes need wings?

Sorry to drag this up from back, but I did some more thinking about the matter, and still am not really satisfied with the result. So planes fly because their wings are airfoil shaped to provide more lift than drag at certain angles right? So it might only take 1 unit of thrust to generate 10 units ...
Wed Mar 14, 2012 3:57 pm UTC
Forum: Mathematics
Replies: 12
Views: 1448

well that would say that c=1 which suggests that the probability everywhere is 1 which also seems kind of crazy because if the probability of something is 1, then it's certain. So how can it be certain everywhere on an interval? To reinforce what gmalivuk said, the PDF of a continuous distribution ...
Wed Mar 14, 2012 3:39 pm UTC
Forum: Mathematics
Replies: 12
Views: 1448

So if the probability is defined only on an interval, then the probability for a 0 width interval must also be 0, making the continuous probability density function 0 everywhere, or perhaps the probability of a 0 width interval is simply undefined? Why then do other functions have continuous probabi...
Wed Mar 14, 2012 3:22 pm UTC
Forum: Mathematics
Replies: 12
Views: 1448

well that would say that c=1 which suggests that the probability everywhere is 1 which also seems kind of crazy because if the probability of something is 1, then it's certain. So how can it be certain everywhere on an interval?
Wed Mar 14, 2012 3:04 pm UTC
Forum: Mathematics
Replies: 12
Views: 1448

I'll assume that you mean for x to be uniformly distributed between 0 and 1. Think about what the CDF means. The CDF evaluated at some point X yields the probability that the random variable x is less than or equal to X. Or, in mathematical terms: CDF(X) = P(x <= X) Now, let's look at the probabili...
Wed Mar 14, 2012 2:32 pm UTC
Forum: Mathematics
Replies: 12
Views: 1448

I'm sure that this is a simple solved problem but I can't figure it out on my own: Given a random number 0<=x<=1, what is the probability distribution of x? Is it 0 everywhere? But because x must be somewhere between 0 and 1 with equal probability, the cumulative distribution function must be a stra...
Sat Jan 21, 2012 6:25 am UTC
Forum: Science
Topic: Why do airplanes need wings?
Replies: 66
Views: 9781

### Re: Why do airplanes need wings?

Yeah obviously I understand these things. But I am trying to address the physical understanding in my head. After a bit of thought, I think what my question boils down to is how does the lift/drag coefficient not violate conservation of momentum? If lift and drag are forces, then they are equal to a...
Sat Jan 21, 2012 5:03 am UTC
Forum: Science
Topic: Why do airplanes need wings?
Replies: 66
Views: 9781

### Why do airplanes need wings?

Bear with me for a second before throwing out the standard grade school answer. If you consider any heavier than air flying object/vehicle. In the most general sense, it stays aloft by pushing air down. Specifically, it needs to constantly accelerate a mass flow of air equal to its weight Some peopl...
Sat Dec 24, 2011 5:34 pm UTC
Forum: Logic Puzzles
Topic: My Family's Secret Santa
Replies: 10
Views: 3731

### Re: My Family's Secret Santa

There are a number of Secret Santa generators available on the internet.
Mon Dec 12, 2011 7:51 pm UTC
Forum: Logic Puzzles
Topic: The motorbike and the car.
Replies: 24
Views: 6088

### Re: The motorbike and the car.

Since this has already been solved, I will attempt to give as simple a solution as possible. No calculator required. Start with the 100 kmph problem. We can do this by simply stretching the distance of the original problem. The car is now traveling 100 kmph and at the same acceleration, the distance...
Fri Nov 25, 2011 11:18 pm UTC
Topic: Definition of Free Will
Replies: 728
Views: 130607

### Re: Definition of Free Will

Free will is intrinsically defined by identity (your sense of self). Consider dividing the universe by your identity. There is everything that is you and there is everything else. By definition then all interactions between you and the universe are at the boundary of your identity. The only informat...
Fri Nov 11, 2011 1:27 pm UTC
Forum: Mathematics
Topic: Proper Team Size handicap at Trivia Night
Replies: 15
Views: 1967

### Re: Proper Team Size handicap at Trivia Night

Well people want to sit and play with their friends and some people have a lot of friends. As an example, say there are six or seven teams of about 5 people and one huge table of 15 people. The huge table wins every single round just by their numbers and everyone else goes home thinking that was a s...