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Type: Posts; User: jemidiah

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1. ## Thread: Difficult, getting a seat pattern from a seat row.

by jemidiah
Replies
13
Views
540

### Re: Difficult, getting a seat pattern from a seat row.

I'm not sure what advice you're hoping to get. You say you want a mathematical "pattern", but that's really vague. You might want an algorithm to choose a subset of a block of seats which satisfies...
2. ## Thread: Expanding a convex hull

by jemidiah
Replies
1
Views
606

### Re: Expanding a convex hull

One approach is to compute Z*OP/|OP| = Z*(P.x - O.x, P.y - O.y)/sqrt((P.x - O.x)^2 + (P.y - O.y)^2) and add it to P. Here OP/|OP| is the unit vector in the direction you wish to move. In your...
3. ## Thread: Calculating Tank Volume

by jemidiah
Replies
5
Views
779

### Re: Calculating Tank Volume

Huh, I apparently missed that "l" repeatedly, sorry about that. You didn't give the important details so I suppose I latched onto a perceived typo instead.
4. ## Thread: Calculating Tank Volume

by jemidiah
Replies
5
Views
779

### Re: Calculating Tank Volume

Well, the volume of a cylinder is pi*r^2*h where r is the radius and h is the height. Your "V = pir^2" is at leaving off the h.
5. ## Thread: Converting between coordinate systems

by jemidiah
Replies
12
Views
769

### Re: Converting between coordinate systems

I think I understand what you want from post #4, which is a function f(x, y) = (u, v) which sends two fixed pairs (x1, y1), (x2, y2) to two fixed pairs (u1, v1), (u2, v2) while scaling distance at a...
6. ## Thread: Converting between coordinate systems

by jemidiah
Replies
12
Views
769

### Re: Converting between coordinate systems

Posting a full example calculation will probably provide enough details for us to describe your situation rigorously and work out the conversion formula. Otherwise it's too vague to really say. As...

by jemidiah
Replies
6
Views
689

Well, my Z is just whatever you're multiplying the dimensions of the image by. So, if the image started at 100x100, doubled to 200x200, and then cut down to 50x50, you would use Z=2 in the first...

by jemidiah
Replies
6
Views
689

Suppose your image has upper left corner (P.X, P.Y). I'll assume the rectangular viewing area has upper left corner (0, 0) and height/width V.height/V.width. Similarly suppose you wish the part of...

by jemidiah
Replies
3
Views
425

### Re: Calculating Distance

I'm not familiar with JavaScript, but apparently variable names are case-sensitive, so you should use .Y in each case instead of .y. Even then, your radiiDifference is 15-15 = 0, so when running "var...

by jemidiah
Replies
3
Views
425

### Re: Calculating Distance

Just glancing at it, you wrote "Math.pow((Pn1.Point.Y - Pn.Point.y) ^ 2)" instead of "Math.pow((Pn1.Point.Y - Pn.Point.y), 2)".
11. ## Thread: Definition and Examples of Binomial | - Algebra

by jemidiah
Replies
1
Views
1,377

### Re: Definition and Examples of Binomial | - Algebra

https://en.wikipedia.org/wiki/Binomial
12. ## Thread: [RESOLVED] Calculate surface area of pyramid

by jemidiah
Replies
3
Views
474

### Re: Calculate surface area of pyramid

To find the height of the four isosceles triangles, draw a right triangle from the vertex to the center of the base to the midpoint of one of the sides. If the sides have length A and the overall...
13. ## Thread: [RESOLVED] Plotting scaled triangle

by jemidiah
Replies
30
Views
2,877

### Re: Plotting scaled triangle

Why do you VB* people do everything the hard way? Weakly typed languages for the win. :)

(Though to be fair, the .NET IDE is really quite nice.)

by jemidiah
Replies
3
Views
439

### Re: Calculate instead of simulate?

Ah, that's far too complicated to hope for an analytic solution. There's also a problem of uniqueness--there are surely quite a few values of your three variables which "on average" with purely...

by jemidiah
Replies
3
Views
439

### Re: Calculate instead of simulate?

More details are needed to give an exact solution; you'll probably end up wanting something like the inverse of a cumulative distribution function.
16. ## Thread: [RESOLVED] Plotting scaled triangle

by jemidiah
Replies
30
Views
2,877

### Re: Plotting scaled triangle

I find the code in post #4 very difficult to interpret--a lot of it doesn't seem to make much sense. The code in post #5 looks pretty close, but I think it should instead be...

'Assume the Sides...
17. ## Thread: [RESOLVED] Reaaranging expression

by jemidiah
Replies
6
Views
738

### Re: [RESOLVED] Reaaranging expression

They're not symbol-for-symbol the same, but yes, they're equal, since 3-c is -(c-3), and 12c-6a is -(6a-12c). I had checked to make sure. You can also have Wolfram Alpha check for symbolic equality,...
18. ## Thread: [RESOLVED] Reaaranging expression

by jemidiah
Replies
6
Views
738

### Re: Reaaranging expression

You're correct, and Wolfram Alpha agrees.
19. ## Thread: [RESOLVED] Generating parallel lines.

by jemidiah
Replies
6
Views
915

### Re: Generating parallel lines.

Minor mistake: "mx = (x2 - x1) / circ2Rad" should be pulled out of the If statement and put right before it. mx is not getting properly reset in the x1=x2 case, which only shows up in the a=0 (or...

by jemidiah
Replies
12
Views
1,527

### Re: Solving Triangles

Note quite. Again the issue is the SSA case, which comes down to the non-invertibility of the sine function on the range 0 to 180. In particular, given a, A, and B, you can compute sin(b), but sin is...

by jemidiah
Replies
12
Views
1,527

### Re: Solving Triangles

You can't do much with just 1 side and its opposite angle. There are certainly many solutions give just those two pieces of information. You should be able to pick a second angle arbitrarily (subject...

by jemidiah
Replies
12
Views
1,527

### Re: Solving Triangles

This is getting at the standard similarity/congruence tests for triangles. Here they are:

AAA: three angles determine the corresponding sides up to an overall scale factor. Since the angles add up...
23. ## Thread: shellsort and selectionsort code help

by jemidiah
Replies
2
Views
1,404

### Re: shellsort and selectionsort code help

This isn't really a math question. It should be in one of the language-specific forums. There are also a zillion code examples of the zillion and one sorting algorithms out there, though they may not...
24. ## Thread: [RESOLVED] solving equation

by jemidiah
Replies
9
Views
1,028

### Re: [RESOLVED] solving equation

Minor thing: I noticed a typo in my second graph's equation from post #8. I had written y = −x² + 21x + 11 instead of y = −x² + 21x + 22. This didn't affect the default Wolfram Alpha view of the...
25. ## Thread: [RESOLVED] solving equation

by jemidiah
Replies
9
Views
1,028

### Re: solving equation

Well, y is 0 at the x-intercepts, since the x-intercepts are on the x-axis, and the x-axis is precisely the line consisting of points whose y-coordinate is 0.

Perhaps this will help? Consider the...
26. ## Thread: [RESOLVED] solving equation

by jemidiah
Replies
9
Views
1,028

### Re: solving equation

I think I'd have to see the question to know what you're trying to do. You again said you needed to "solve for x", and I've told you how to solve for x in terms of y. If you mean you need to solve...
27. ## Thread: [RESOLVED] solving equation

by jemidiah
Replies
9
Views
1,028

### Re: solving equation

You wrote an expression, not an equation, so what do you mean by it "seems insoluble without a value for y"?

To take a simpler example, start with y=x^2. Doing the same operation, i.e. saying x^2...
28. ## Thread: [RESOLVED] solving equation

by jemidiah
Replies
9
Views
1,028

### Re: solving equation

Well, if you want to solve your equation for x in terms of y, you'll have to use the quadratic formula, and there are two "branches" of solutions in general (the function is not invertible in...
29. ## Thread: [RESOLVED] Round-about way to get even distribution using Random functions.

by jemidiah
Replies
4
Views
1,346

### Re: Round-about way to get even distribution using Random functions.

Oh, I agree my solution is easy to implement with a for loop, it's just cleaner and (potentially) faster to use a linked list/queue style data structure, at least if there are often many unused spots...
30. ## Thread: [RESOLVED] Round-about way to get even distribution using Random functions.

by jemidiah
Replies
4
Views
1,346

### Re: Round-about way to get even distribution using Random functions.

Yeah, I'm not a big fan of the two methods you suggested either. The first would make earlier entities *much* more likely to be chosen than later ones, while the second would make the last entity...
31. ## Thread: radius of circumcircle from 3 points formula... can someone explain?

by jemidiah
Replies
8
Views
1,454

### Re: radius of circumcircle from 3 points formula... can someone explain?

That article is nice and brief, and it gives some notion of what the parts of Heron's formula individually "mean". It does something quite similar to what my proof does, but with the incircle rather...
32. ## Thread: radius of circumcircle from 3 points formula... can someone explain?

by jemidiah
Replies
8
Views
1,454

### Re: radius of circumcircle from 3 points formula... can someone explain?

@boops boops: for what it's worth, I made an effort to avoid Heron's formula since it seemed like its use just pushes the problem farther down the line--why is Heron's formula true? On the other hand...
33. ## Thread: radius of circumcircle from 3 points formula... can someone explain?

by jemidiah
Replies
8
Views
1,454

### Re: radius of circumcircle from 3 points formula... can someone explain?

First, here's why the circumcenter exists. Take two sides of a triangle and consider their perpendicular bisectors. Since the sides are not parallel, neither are the perpendicular bisectors, so they...
34. ## Thread: [RESOLVED] drawing random triangle

by jemidiah
Replies
10
Views
1,254

### Re: drawing random triangle

Just to be clear, my comment about precision was directed at how precisely you wanted to draw "the maximum sized scale triangle within the bounding rectangle [subject to some given angles]", rather...
35. ## Thread: [RESOLVED] drawing random triangle

by jemidiah
Replies
10
Views
1,254

### Re: drawing random triangle

The complexity of what you want depends a lot on how precise you want it all to be and what you're willing to say is "good enough". For instance, your "acute" case in post #1 allows non-acute...
36. ## Thread: [RESOLVED] Rotating 3d Object by Axis

by jemidiah
Replies
7
Views
1,619

### Re: Rotating 3d Object by Axis

@dday9: cool beans.

Totally understandable, though in this case there was a very easy check besides looking at the original source code. The matrix form of the operation needed to have...
37. ## Thread: [RESOLVED] Rotating 3d Object by Axis

by jemidiah
Replies
7
Views
1,619

### Re: Rotating 3d Object by Axis

I see one big mistake still in #3, namely the "- x" should be "+ x". That would produce extremely erratic results.

I disagree with passel in that I think the integer-based coordinates for your...
38. ## Thread: [RESOLVED] Gaussian Sigma and Pascal's Triangle

by jemidiah
Replies
2
Views
1,237

### Re: Gaussian Sigma and Pascal's Triangle

You seem to be referring to the fact that the rows of Pascal's triangle, when plotted after normalization, look very much like a normal distribution, especially as you take longer and longer rows....
39. ## Thread: [RESOLVED] Average from percentage?

by jemidiah
Replies
4
Views
640

### Re: [RESOLVED] Average from percentage?

Ah, my mistake. That makes the computation easier. Since 0 < N < 100, we may evidently assume every such sequence terminates, since a non-terminating sequence occurs with 0 probability. Each sequence...
40. ## Thread: [RESOLVED] Average from percentage?

by jemidiah
Replies
4
Views
640

### Re: [RESOLVED] Average from percentage?

Unless I'm really, really misunderstanding your question, it's not (N/100)M times. For instance, at N=100, this gives M, but as you say it should obviously give infinity. As I understand it, you...
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