Depth of a quantum circuit Updated +Created
This is an important metric, because it takes some time for the quantum operations to propagate, and so the depth of a circuit gives you an idea of how long the coherence time a hardware needs to support a given circuit.
Numerical analysis Updated +Created
Techniques to get numerical approximations to numeric mathematical problems.
The entire field comes down to estimating the true values with a known error bound, and creating algorithms that make those error bounds asymptotically smaller.
Not the most beautiful field of pure mathematics, but fundamentally useful since we can't solve almost any useful equation without computers!
The solution visualizations can also provide valuable intuition however.
Important numerical analysis problems include solving:
Aum Shinrikyo Updated +Created
Australian company Updated +Created
Automated theorem proving Updated +Created
AGI-complete in general? Obviously. But still, a lot can be done. See e.g.:
This construction takes as input:and it produces an elliptic curve over a finite field of order as output.
The constructions is used in the Birch and Swinnerton-Dyer conjecture.
To do it, we just convert the coefficients and from the Equation "Definition of the elliptic curves" from rational numbers to elements of the finite field.
For example, suppose we have and we are using .
For the denominator , we just use the multiplicative inverse, e.g. supposing we have
where because , related: math.stackexchange.com/questions/1204034/elliptic-curve-reduction-modulo-p
Relationship between the quotient group and direct products Updated +Created
Although quotients look a bit real number division, there are some important differences with the "group analog of multiplication" of direct product of groups.
If a group is isomorphic to the direct product of groups, we can take a quotient of the product to retrieve one of the groups, which is somewhat analogous to division: math.stackexchange.com/questions/723707/how-is-the-quotient-group-related-to-the-direct-product-group
The "converse" is not always true however: a group does not need to be isomorphic to the product of one of its normal subgroups and the associated quotient group. The wiki page provides an example:
Given G and a normal subgroup N, then G is a group extension of G/N by N. One could ask whether this extension is trivial or split; in other words, one could ask whether G is a direct product or semidirect product of N and G/N. This is a special case of the extension problem. An example where the extension is not split is as follows: Let , and which is isomorphic to Z2. Then G/N is also isomorphic to Z2. But Z2 has only the trivial automorphism, so the only semi-direct product of N and G/N is the direct product. Since Z4 is different from Z2 × Z2, we conclude that G is not a semi-direct product of N and G/N.
TODO find a less minimal but possibly more important example.
I think this might be equivalent to why the group extension problem is hard. If this relation were true, then taking the direct product would be the only way to make larger groups from normal subgroups/quotients. But it's not.
RSA (cryptosystem) Updated +Created
Based on the fact that we don't have a P algorithm for integer factorization as of 2020. But nor proof that one does not exist!
The private key is made of two randomly generated prime numbers: and . How such large primes are found: how large primes are found for RSA.
The public key is made of:
Given a plaintext message m, the encrypted ciphertext version is:
c = m^e mod n
This operation is called modular exponentiation can be calculated efficiently with the Extended Euclidean algorithm.
The inverse operation of finding the private m from the public c, e and is however believed to be a hard problem without knowing the factors of n.
However, if we know the private p and q, we can solve the problem. As follows.
First we calculate the modular multiplicative inverse. TODO continue.
Russia Updated +Created
West Asia Updated +Created
Average length of a Snakes and Ladders game Updated +Created
Since Snakes and Ladders is nothing but a Absorbing Markov chain, the results are exactly the same as for that general problem.
www.jstor.org/stable/3619261: How Long Is a Game of Snakes and Ladders? by Althoen, King and Schilling (1993), paywalled.
C6 Oxford physics course Updated +Created
Video 1.
A very honest review of my Oxford University master's degree (theoretical physics at keble college) by alicedoesphysics (2020)
Source. Basically all her courses are from the Mathematical Institute of the University of Oxford, and therefore show up at the Moodle of the Oxford Mathematics Institute of Oxford.
C7.4 Oxford physics course Updated +Created
Climate change Updated +Created
Information technology Updated +Created
Bell's theorem Updated +Created
Basically a precise statement of "quantum entanglement is spooky".

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