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Closed 10 years ago.
I have N points. Each point has X and Y coordinates.
I need to find X and Y of center of mass this points. Can you give me an algorithm to accomplish this task?
Is there something wrong with just taking the weighted average by mass?
for each point n
{
totalmass += n.mass
totalx += n.x*n.mass
totaly += n.y*n.mass
}
center = (totalx/totalmass,totaly/totalmass)
add additional dimensions as appropriate.
Related
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Closed 10 years ago.
What's the easiest way to get two nibbles (as Integers) from a byte in Ruby?
If the "byte" is a number between 0 and 255:
n1, n2 = (byte & 0xf0) >> 4, byte & 0x0f
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Closed 10 years ago.
I came across this question and couldn't figure out how to approach it. Can someone please help me out? The question is-
Add numbers in base n (not any of the popular ones like 10, 16, 8 or 2 - I hear that Charles Simonyi, the inventor of Hungarian Notation, favors -2 when asking this question).
I just need the idea.
You didn't specify a language, but you could just convert the base n number into a standard integer and add it.
Suppose base N number = '...d2d1d0' where di = the i'th digit.
Number = ... d2 * N^2 + d1 * N^1 + d0 * N^0
Then just add the numbers as usual.
Idea: it looks like hashing, but in hash function you can't use negative numbers.
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Closed 10 years ago.
I have yaw, pitch and roll from an object and i need to transform it into vectorDir and vectorUp. Someone an idea of how to do it?
I would convert the Euler angles (yaw, pitch and roll) into a rotation matrix M. Follow this answer for example.
It is not 100% clear what you need but you it is one of the followings.
You get vectorDir by multiplying the column vector x=[1,0,0] by either M or its transpose.
You get vectorUp by multiplying the column vector z=[0,0,1] by either M or its transpose.
Note. Euler angles are evil, they screw up the stability of your app, see for example
Strange behavior with android orientation sensor,
Reducing wiimote pitch/roll variations.
They are not useful for interpolation either.
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Closed 11 years ago.
Please help solve this:
Telephone numbers are often given out as a word representation, so that they are easy to remember. For example if my number is 4357, the text given is HELP. There could be many other possibilities with the same digits, most of which do not make sense.
Write a space-and-time-optimal function that can, given a phone number, print the possible words that can be formed from it.
Based on the detailed explanation in the comment this should be a simple permutation combination problem:
Each digit will have a number of characters associated to it (example 4 could mean either of G,H or I) and then for a combination of digits the permutation can be computed.
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Closed 11 years ago.
There is a 3D grid with cells for which we define its value (0 or 1) as F(i,j,k)=F(i-1,j,k) XOR F(i,j-1,k) XOR F(i,j,k-1), base cases are F(0,0,0)=1 and F(x,y,z)=0 for x < 0 or y < 0 or z < 0 (if at least one parameter is negative).
We want to count amount of cells with F()=1 in the cube with corners (0,0,0) and (N, M, K). Dimensions are about 2^30.
I'm looking for the fast approach on this problem.