4,020 reputation
1023
bio website
location
age
visits member for 3 years, 3 months
seen 19 hours ago

Dec
2
reviewed Close Conjecture about some rings and roots of unity.
Dec
2
comment Determining Ambiguity in Context Free Grammars
An even simpler ambiguous string is $()$.
Nov
30
reviewed Close Find $g$ such that $g'(0) = 2, g(x + y) = e^yg(x) + e^xg(y)$
Nov
30
reviewed Close Complete the square.
Nov
30
revised What is the minimum number of locks on the cabinet that would satisfy these conditions?
Add missing "fi" - I suspect this was copy-pasted from a PDF which used a ligature
Nov
28
reviewed No Action Needed Cumulative distribution function word problem
Nov
27
answered 9-Rook problem in 3D / weak version of sudoku
Nov
27
reviewed Approve suggested edit on Ice cream vendor problem
Nov
25
comment Prove that every practical number is either a power of two or a power of two times a non-trivial polygonal number
@half-integerfan, I've added lists of 1000 and 1000000 practical numbers to my personal site at cheddarmonk.org/maths/practical_numbers/… and obvious substitution. I will refresh my memory on the current comment submission process for OEIS at a later date.
Nov
9
reviewed Close What does $(C-D)\cup (D-C)$ mean?
Nov
8
comment Representing everywhere a camera can see as a matrix
you can test a point $Q=(x_Q, y_Q, z_Q)$ against the near and far planes by simply comparing $z_Q$ to the near and far clipping distances; you can clip against the side planes by comparing $x_Q / z_Q$ to $\pm\tan (\theta_w/2)$ where $\theta_w$ is the angular width; and you can clip against the top and bottom planes by comparing $y_Q / z_Q$ to $\pm\tan (\theta_h/2)$ where $\theta_h$ is the angular height.
Nov
8
comment Representing everywhere a camera can see as a matrix
@Imray, the frustrum is bounded by 6 planes. Testing which side of a plane a point is on comes down to looking at the sign of a dot product. (E.g. if the plane is defined by a point $P$ in the plane and its normal $N$ then you can test which side a point $Q$ is by looking at the sign of $(Q-P).N$). It wouldn't surprise me, though, if actual implementations take a different approach. If you transform the world such that your camera is positioned at the origin and looks along the $z$-axis, with the up vector pointing along the $y$-axis, then (cont)
Nov
8
reviewed Close Probability of taking the right key at the tenth pick
Nov
8
answered Representing everywhere a camera can see as a matrix
Nov
7
reviewed Close Mean Value Theorem with a constant
Nov
7
comment Probabilty to win in die rolling game
Thanks for editing to add your ideas. The point at which you're going wrong is to interpret the question as asking for a probability which relates to a single die roll. It's actually asking for the probability that you lose on the first die roll (which you correctly state to be $k/N$), or that you lose on your next die roll, or a subsequent one. I hope that makes it clearer what you should be recursing on.
Nov
7
reviewed Edit and Reopen Probabilty to win in die rolling game
Nov
7
revised Probabilty to win in die rolling game
Formatting and linguistic style
Nov
6
reviewed Close On finite subring of a division ring
Nov
5
comment Dead presidents
I think the only reasonable answer to this question is that it's not well posed. If you're supposed to pretend you don't know the death dates, shouldn't you also pretend that you don't know how many are still alive? So the person who posed it should specify precisely what information you have as prior knowledge.