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Nov
28
comment Such a thing as a circular arithmetic progression?
@coffeemath: Yep, I noticed that too. Maybe they're not specifically studied and that's why? It definitely would make it easier to prove properties about them.
Nov
28
revised Such a thing as a circular arithmetic progression?
added 1 characters in body
Nov
28
awarded  Student
Nov
28
asked Such a thing as a circular arithmetic progression?
Nov
11
accepted Negative coefficients and Bezout's identity
Nov
11
comment Negative coefficients and Bezout's identity
This is what I was confused about, looks safe: math.stackexchange.com/questions/37806/…
Nov
11
comment Negative coefficients and Bezout's identity
I guess the question here is whether $gcd(a, b)$ and $gcd(a, -b)$ produce the same bezout coefficients, and thus the same $x, y, k$. Although if it did that would seem to imply that when $ax + by = gcd(a, b)*k$ is true that $ax - by = gcd(a, b) * k$ is also true, which would mean you could toggle the +/- sign in Bezout's identity, which doesn't seem right.
Nov
10
awarded  Commentator
Nov
10
awarded  Editor
Nov
10
comment Negative coefficients and Bezout's identity
Added a note about $k$, in the main question so you could better see what I mean.
Nov
10
revised Negative coefficients and Bezout's identity
added 93 characters in body
Nov
10
comment Negative coefficients and Bezout's identity
Substitution does make things more clear but doesn't seem to get me all the way there. I can write $ax_1 + by_1 = gcd(a, b) * k_1$, and I can say $c = -b$ and use substitution to get $ax_2 + cy_2 = gcd(a, c) * k_2$, then plug $-b$ back in for $c$ and get $ax_2 - by_2 = gcd(a, -b) * k_2 = gcd(a, b) * k_2$, but it's unclear what the relationship between $x_1, y_1, k_1$ and $x_2, y_2, k_2$ are. $x_2$ and $y_2$ correspond to the $d$ and $f$ in the original example and are the numbers I actually want, but the identity/algo only let me compute $x_1$ and $y_1$, and I don't see how to substitute back.
Nov
10
asked Negative coefficients and Bezout's identity
Nov
3
comment Euclidean Algorithm vs Factorization
Just have your brother try both on a large number.
Oct
16
comment Representing circular bitwise shift mathematically
I think I get it, it makes more sense to me if the floor is multiplied out so you get $floor(x/2^{m-1}) - 2^mfloor(x/2^{m-1})$. It's a conditional add of 1 to flip the bit in the lowest place if needed, and a conditional subtraction of the $2^m$ if it was needed. It'd be even clearer if we stored $floor(x/2^{m-1})$ in value called 'highbitset' ;) That's nifty.
Oct
16
comment Representing circular bitwise shift mathematically
I get that checking for the value being bigger than $2^{m-1}$ is checking whether the high bit is set, and I get that because we did $2x$ not modulo we need to somehow cancel out the 1 that may be in the 33rd bit, and somehow set the least significant bit, but that addition appears to kill two birds with one stone somehow.
Oct
16
comment Representing circular bitwise shift mathematically
Could you explain how you derived this? Based on how left circular shift is usually implemented in code, ((x << 1) | (x >> (m - 1))), I can see the $2x$ as being the left shift, but I'm confused how the rest becomes equivalent to the right shift and the bitwise or. $floor(x/2^{m−1})$ will only ever be 0 or 1, since in the m-bit unsigned integers nothing is twice as big as $2^{m−1}$ since it wraps to 0. So we're conditionally deciding whether to add $(1−2^m)$ based on whether our starting value is greater than $2^{m−1}$. But passed that I'm not sure why adding $(1−2^m)$ does the trick.
Oct
13
awarded  Scholar
Oct
13
awarded  Supporter
Oct
13
comment Why don't all elements of an arithmetic progression divide the lcm of the start and step?
Ah, so the problem isn't that they don't work with ∀ and ∃, it's that they only work with ∀ and ∃.