Search found 46 matches

by sgfw
Thu Mar 12, 2015 11:28 pm UTC
Forum: Science
Topic: Effect of a force on angular velocity?
Replies: 5
Views: 1809

Re: Effect of a force on angular velocity?

You can, however, decompose it. If you see an object with both linear and rotational acceleration, you can calculate the force applied to the CoM and a "free moment", an opposing force couple that produces a pure rotation. It's often used in inverse dynamics for studying kinetics of robot...
by sgfw
Thu Mar 12, 2015 4:45 pm UTC
Forum: Science
Topic: Effect of a force on angular velocity?
Replies: 5
Views: 1809

Effect of a force on angular velocity?

I'm in a physics class, and I have learned that if a force is applied to an object on the center of mass, then the object does not spin, but if a force is applied to another part of the object, then it will spin. How do you calculate how a force would affect an object both rotationally and directly?
by sgfw
Thu Nov 06, 2014 11:46 pm UTC
Forum: Mathematics
Topic: Multiply 2 terminating numbers and get a repeating decimal?
Replies: 6
Views: 2708

Re: Multiply 2 terminating numbers and get a repeating decim

Okay, so is wolfram alpha doing the multiplication/base conversion incorrectly, or does the number just repeat for an absurdly long time before terminating?
by sgfw
Thu Nov 06, 2014 10:29 pm UTC
Forum: Mathematics
Topic: Multiply 2 terminating numbers and get a repeating decimal?
Replies: 6
Views: 2708

Multiply 2 terminating numbers and get a repeating decimal?

The two terminating numbers in question are 0.3333331901677568 and 1.0000004294967296. When multiplied in base 10, they result in the terminating number 0.33333333333327184418642096816128. The problem arises when they are multiplied in base 4294967295. As you can see, both 0.3333331901677568 and 1.0...
by sgfw
Sun Oct 19, 2014 3:51 pm UTC
Forum: Computer Science
Topic: Newton-Raphson division for a non-binary base?
Replies: 4
Views: 3569

Re: Newton-Raphson division for a non-binary base?

Just as base 10 uses digits 0 to 9 and has no digit symbol with value 10, base 4294967296 uses digits 0 to 4294967295, exactly the full range of what an unsigned 32-bit integer can hold, and never needs any digit to hold value 4294967296. Oh, I guess you're right. I lost track of the reason I am us...
by sgfw
Sat Oct 18, 2014 7:48 pm UTC
Forum: Computer Science
Topic: Newton-Raphson division for a non-binary base?
Replies: 4
Views: 3569

Re: Newton-Raphson division for a non-binary base?

Thanks! Also, I'm using base 4294967295 instead of 4294967296 because an unsigned integer in c++ can't hold 4294967296, because it would take 33 bits. I could store it in an unsigned long, but that would be inefficient.
by sgfw
Thu Oct 16, 2014 8:12 pm UTC
Forum: Computer Science
Topic: Newton-Raphson division for a non-binary base?
Replies: 4
Views: 3569

Newton-Raphson division for a non-binary base?

I'm trying to make an arbitrary precision float class in C++, and it stores the information in a linked list of unsigned integers as digits in base 4294967295. I chose this number because I thought it was a good number as far as processing required for an operation vs. memory efficiency. I have made...
by sgfw
Sun Sep 14, 2014 9:54 pm UTC
Forum: Coding
Topic: C++ question about non-integer parts of large doubles
Replies: 7
Views: 3989

Re: C++ question about non-integer parts of large doubles

Thanks! I had no idea you could set the precision like that. That's helpful.
by sgfw
Sun Sep 14, 2014 6:24 pm UTC
Forum: Coding
Topic: C++ question about non-integer parts of large doubles
Replies: 7
Views: 3989

Re: C++ question about non-integer parts of large doubles

I think you've got the wrong analysis. 4294967295 is a 32-bit number, so in the worst case you wipe out 32-bits from the 53-bit mantissa. You should still have 21-bits of mantissa after the calculation. I don't really know that much about this, but when I run a code like this one: double d = 0.2432...
by sgfw
Sat Sep 13, 2014 11:55 pm UTC
Forum: Coding
Topic: C++ question about non-integer parts of large doubles
Replies: 7
Views: 3989

C++ question about non-integer parts of large doubles

Okay, so I have this problem, where I need to multiply a float (which would always be between 0 and 1) by 4294967295 and get the non-integer part. Generally, this could be done with double a = whatever; double b = a*4294967295.; answer = b - (int)b but the number when multiplied by 4294967295 is too...
by sgfw
Fri Sep 05, 2014 8:54 pm UTC
Forum: Coding
Topic: Help with a simple fortran program
Replies: 2
Views: 2385

Re: Help with a simple fortran program

Isn't "not equal" /= instead of != in Fortran?


Yeah, it looks like that was the problem. I guess I kind of jumped right in to the language and assumed it had that operator. Thanks!
by sgfw
Fri Sep 05, 2014 8:36 pm UTC
Forum: Coding
Topic: Help with a simple fortran program
Replies: 2
Views: 2385

Help with a simple fortran program

I just started programming in fortran, this is my second program after "hello world," and my compiler is mad at me. This is the program: program collatz implicit none real a read *, a print *, a do while (a != 1.) if (mod(a, 2.) == 0) then a = a/2 else a = a*3 + 1 end if print *, a end do ...
by sgfw
Sat Jul 26, 2014 2:26 pm UTC
Forum: Coding
Topic: Difficulty with tree restructuring
Replies: 5
Views: 2824

Re: Difficulty with tree restructuring

That's not exactly what I'm going for, It would be helpful if there was a way to do it such that the function is not made to make only one replacement, but instead is capable of making any specified replacement it is given. However, this is a nice new way to look at the entire problem, so I'll see i...
by sgfw
Fri Jul 25, 2014 6:20 pm UTC
Forum: Coding
Topic: Difficulty with tree restructuring
Replies: 5
Views: 2824

Re: Difficulty with tree restructuring

I don't really have a good idea of what you tried and what you think doesn't work (and what does) I can't imagine a solution to this problem that isn't recursive, so I started by making a program that starts at the top, and goes down every branch looking for a chain of nodes that is the same as the...
by sgfw
Fri Jul 25, 2014 5:05 pm UTC
Forum: Coding
Topic: Funniest/Most Annoying Code Comments
Replies: 662
Views: 132930

Re: Funniest/Most Annoying Code Comments

The source for this website has an ASCII pterodactyl in the comments.
by sgfw
Fri Jul 25, 2014 4:51 pm UTC
Forum: Coding
Topic: Difficulty with tree restructuring
Replies: 5
Views: 2824

Difficulty with tree restructuring

I'm making a CAS program in python and I have a class for expressions that is organized as a tree with a node for each operator ('+', '-', '*', '/', '^') and one for several functions ('sin', 'cos', 'log', etc) It works for a lot of purposes, but I would really like to make a function to "restr...
by sgfw
Sat Jul 12, 2014 1:57 am UTC
Forum: Mathematics
Topic: Need help with understanding equations
Replies: 6
Views: 2036

Re: Need help with understanding equations

Pretty much reverse PEMDAS. But that's not the way I think about it. I think about it more like this: Numbers that are being added or subtracted are pretty far away from each other, so they aren't really that "attached", and can be moved first, unless they are being held in by parenthesis....
by sgfw
Thu Jul 10, 2014 7:46 pm UTC
Forum: Mathematics
Topic: Derivative of a function of two variables?
Replies: 6
Views: 1857

Re: Derivative of a function of two variables?

The last two terms should be multiplied, not added, but yeah, that's the idea.


Yeah, I think that was a typo.
by sgfw
Thu Jul 10, 2014 7:36 pm UTC
Forum: Mathematics
Topic: Derivative of a function of two variables?
Replies: 6
Views: 1857

Re: Derivative of a function of two variables?

Would the derivative of a function of three variables f(g1(x), g2(x), g3(x)) be df/dg1 * dg1/dx + df/dg2 * dg2/dx + df/dg3 + dg3/dx?
by sgfw
Thu Jul 10, 2014 7:21 pm UTC
Forum: Mathematics
Topic: Derivative of a function of two variables?
Replies: 6
Views: 1857

Derivative of a function of two variables?

I know that the derivative of f(g(x)) is f'(g(x))*g'(x), but what about something like f(g(x), h(x))? Is there any way to determine this derivative without more information about any of the functions? Thanks.
by sgfw
Sat Jul 05, 2014 10:58 pm UTC
Forum: Mathematics
Topic: Graph formula help
Replies: 8
Views: 2223

Re: Graph formula help

Possibly a scaled error function would work for your purposes?
by sgfw
Sun Jun 29, 2014 4:40 pm UTC
Forum: Mathematics
Topic: Domain of the regularized incomplete beta function?
Replies: 0
Views: 2035

Domain of the regularized incomplete beta function?

I've been making an algorithm for the regularized incomplete beta function, which pretty much just uses the continued fraction given here , along with the property that I x (a, b) = I 1-x (b, a), which works, mostly. The algorithm has an error when a or b are negative integers, which makes sense bec...
by sgfw
Thu Jun 19, 2014 1:39 am UTC
Forum: Science
Topic: I think I understand why black holes are weird
Replies: 33
Views: 5710

Re: I think I understand why black holes are weird

But when you reach the surface of the Earth, this breaks down; the planet itself gets in your way - you have to tunnel into the planet to get closer to its centre. But now there's some planet above you, pulling you away. In fact, when you reach the centre, there's as much pulling you "up"...
by sgfw
Wed Jun 18, 2014 11:31 pm UTC
Forum: Science
Topic: I think I understand why black holes are weird
Replies: 33
Views: 5710

Re: I think I understand why black holes are weird

Because a black hole is a singularity, an infinitely small point of infinite density, where spacetime is infinitely warped. The article says a black hole is crushed to zero volume by infinite gravity, but this raises more questions: If black holes had infinite gravity, then 1) Wouldn't they need to...
by sgfw
Wed Jun 18, 2014 11:15 pm UTC
Forum: Science
Topic: I think I understand why black holes are weird
Replies: 33
Views: 5710

Re: I think I understand why black holes are weird

This is the sort of thing I'm confused about: Why do the graphics for stars and such have bottoms, but the one for black holes doesn't? What makes a black hole intrinsically so different from everything else? I recognize that it has a proportionately more powerful gravitational field in a smaller sp...
by sgfw
Wed Jun 18, 2014 8:35 pm UTC
Forum: Science
Topic: I think I understand why black holes are weird
Replies: 33
Views: 5710

Re: I think I understand why black holes are weird

Xenomortis wrote:How much relativity do you know?


I have a rudimentary understanding
by sgfw
Wed Jun 18, 2014 8:00 pm UTC
Forum: Science
Topic: I think I understand why black holes are weird
Replies: 33
Views: 5710

I think I understand why black holes are weird

For I very long time, I could never really understand what was so weird about black holes. I always just thought of them as a really massive and very dense object that had a proportionately powerful gravitational field. If it were massive enough, the gravitational field would obviously become powerf...
by sgfw
Tue Feb 18, 2014 12:39 am UTC
Forum: Mathematics
Topic: Notation and properties of nested functions?
Replies: 19
Views: 3808

Re: Notation and properties of nested functions?

the conjecture hinges on what happens to trajectories mod 2, throwing that out doesn't seem a strong start I'm not really sure what your post is saying- I don't know what "adic" means (something to do with prime numbers?). But anyway, I think I understand what you are saying here, and the...
by sgfw
Mon Feb 17, 2014 4:20 pm UTC
Forum: Mathematics
Topic: Notation and properties of nested functions?
Replies: 19
Views: 3808

Re: Notation and properties of nested functions?

There's at least one cycle you've missed: -2 -> -1 -> -2... but it might be a repulsive attractor.


Yeah, so I guess it doesn't work completely with all negative numbers. Oh well, it's still interesting.
by sgfw
Mon Feb 17, 2014 3:07 pm UTC
Forum: Mathematics
Topic: Notation and properties of nested functions?
Replies: 19
Views: 3808

Re: Notation and properties of nested functions?

Speaking of interesting things, I noticed something. The collatz conjecture only works for positive integers, and the generalized form I made [which I now simplified to x/2 + (5*x+2)*mod(x/2, 1)] when iterated seems to work for all real numbers except zero. All positive numbers approach the cycle 1,...
by sgfw
Mon Feb 17, 2014 2:11 pm UTC
Forum: Mathematics
Topic: Notation and properties of nested functions?
Replies: 19
Views: 3808

Re: Notation and properties of nested functions?

I'm actually making an attempt to prove the collatz conjecture. The function f(x) = (5/2)x^2 + (3/2)x - (5x+2)(floor(x/2)) will output x/2 is x is even and 3x + 1 if x is odd. If I can find a generalized form of that function nested n times, I may be able to find the limit as n approaches infinity, ...
by sgfw
Mon Feb 17, 2014 12:23 am UTC
Forum: Mathematics
Topic: Notation and properties of nested functions?
Replies: 19
Views: 3808

Re: Notation and properties of nested functions?

Are you asking for this sort of notational shorthand, or are you interested in the particular question I'm trying to learn what I can about this sort of thing so that I can come closer to solving the problem. Of course is someone can solve it for me, then that would be great. Really, what I'm looki...
by sgfw
Sun Feb 16, 2014 10:30 pm UTC
Forum: Mathematics
Topic: Notation and properties of nested functions?
Replies: 19
Views: 3808

Notation and properties of nested functions?

Say you have a function, f(x). Is there any easy way to denote f(f(f(...f(x)...))), nested n times? Also, are there any handy properties to help simplify things like this? Some are obvious, such as: if f(x) is in the form x + c, then nested n times it would be x + c*n if f(x) is in the form c*x, the...
by sgfw
Sun Feb 09, 2014 12:11 am UTC
Forum: Mathematics
Topic: A probability(?) problem
Replies: 13
Views: 3711

A probability(?) problem

I'm not sure if this is technically probability or not, but I have been puzzling about it with my friend to no avail. Known: -There is a dice with a finite number of sides. This number may or may not be random. -Every side of the dice has a finite positive number on it. These numbers may or may not ...
by sgfw
Sun Jan 12, 2014 12:11 am UTC
Forum: Coding
Topic: Python 3: Defining a class type inside a class?
Replies: 2
Views: 2258

Re: Python 3: Defining a class type inside a class?

Is there a reason you can't just do "isinstance(b, C)"?


Yes- I didn't know that existed. Thanks for the help, that solved my problem.
by sgfw
Sat Jan 11, 2014 10:43 pm UTC
Forum: Coding
Topic: Python 3: Defining a class type inside a class?
Replies: 2
Views: 2258

Python 3: Defining a class type inside a class?

So, I have a code that resembles a more complicated version of this: class C: t = type(C(1)) def __init__(self, a): self.whatever = a def somefunction(self, b): if type(b) == C.t: self.whatever = f1(b) else: self.whatever = f2(b) My problem is with the line "t = type(C(1))" I need a functi...
by sgfw
Tue Dec 24, 2013 12:15 am UTC
Forum: Mathematics
Topic: Is it possible to prove that something is unprovable?
Replies: 24
Views: 6513

Is it possible to prove that something is unprovable?

Mathematicians prove the rules that they use all the time, and some things have been proven false, as well. I can't think of any examples, but do you suppose it would ever be possible to prove that the validity of a conjecture is unprovable either way? Would it be accepted as a rigorous proof? How d...
by sgfw
Mon Dec 09, 2013 8:31 pm UTC
Forum: Mathematics
Topic: Exceptions to sqrt(a*b) = sqrt(a)*sqrt(b)
Replies: 4
Views: 3625

Exceptions to sqrt(a*b) = sqrt(a)*sqrt(b)

As is very well known, the rule does not apply when and b are negative: sqrt(-4)*sqrt(-9) = 2*i*3*i = -6 sqrt(-4*-9) = sqrt(36) = 6 A lot of people I have talked to dismiss this as a simple exception to a rule, but it is definitely more complicated than that. The rule in the subject is just a more s...
by sgfw
Sat Nov 16, 2013 8:01 pm UTC
Forum: The Help Desk
Topic: What happens if I delete internet explorer from the registry
Replies: 5
Views: 3771

What happens if I delete internet explorer from the registry

Internet explorer has conflicted with other programs many times, and I don't like it at all as a browser. I have deleted the shortcuts and the .exe, but it is still in the registry, and is still causing problems. Would it mess anything up if I deleted the following from the registry? HKEY_CURRENT_US...
by sgfw
Sun Oct 13, 2013 1:09 pm UTC
Forum: Mathematics
Topic: The ambiguity of indefinite integrals
Replies: 12
Views: 5409

Re: The ambiguity of indefinite integrals

So, that makes the C kind of misleading, doesn't it? If it's actually a function?

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