thorel
Joined 13 years ago
Joined 13 years ago
It is note quite correct that the finite field of order p^k is the set of residues modulo p^k when k > 1. Instead this field is obtained as a splitting field of the field of order p (which is the set of residues mod p).
There, the obstacle is in some sense of a simplest nature: if your set of axioms admits a countable model, then it admits models of all infinite cardinalities. In other words, it shows that there is something fundamentally impossible in trying to capture an infinite structure (like numbers) by finite means (e.g. recursively axiomatizable).
An alternative approach is purely syntactic and sees a logical system as collection of valid transformation rules that can be applied to the axioms. In this view, a sentence is true if it can be obtained from the axioms by applying a sequence of valid transformation rules. This purely syntactic notion of truth is known as “provability”.
Then the key question is to ask whether the two notions coincide: one way to state Godel's first incompleteness theorem is that it shows the two notions do not coincide.
This being said, your intuition is absolutely correct, the crux of the issue is with ‘this‘. What mathematicians realized is that if you are not careful with your choice of axioms, the resulting logical system becomes too “powerful” in the sense that it becomes self-referential: you can construct sentences that refer to themselves in a self-defeating manner.
As others have mentioned, this is the idea underlying Gödel's incompleteness theorem but also, to some extent, Russel's paradox that came before and is what the article is referring to. In Russel's paradox, the contradiction comes from constructing the set of all sets that contain themselves.
> Really, it’s harder than this picture suggests, because many experiences are based on other students. If I want you as my project partner but you want to forget I exist, then something has to give.
Perhaps the most famous example is provided by the Lp spaces [1] consisting of functions whose pth power is absolutely integrable. For p≥1, these spaces are Banach spaces (complete normed spaces) but it is only when p=2 that the norm is associated with an inner product.
The significance of this paradigm shift is that it allowed mathematicians to apply some of the geometric intuition developed from the study of finite-dimensional spaces (such as the 3D Euclidean space) to difficult questions involving functions, such as the existence of solutions to certain differential equations.
The history of this change of perspective is absolutely fascinating and can be traced back to the end of the 19th century and beginning of the 20th century. At the time, work on axiomatic foundations of mathematics was driving a systematization of the study of mathematical objects by capturing their structure with a concise list of axioms. This is for example how the concept of an abstract vector space was born, encompassing not only Euclidean spaces but also infinite-dimensional spaces of functions.
An early reference already demonstrating this change of perspective, albeit in a primitive form, is a memoir by Vito Volterra from 1889 [1]. The PhD thesis of Maurice Fréchet from 1906 [2] is arguably the work that was most influential in crystalizing the new paradigm and presenting it in a modern form that served as a key reference for the first half of the 19th century. Of course, these are only two among a multitude of works around that time. Looking at later developments in the 19th century, it is hard not to also mention the book by Stefan Banach from 1932 [3].
[1] https://projecteuclid.org/journals/acta-mathematica/volume-1...
[2] https://zenodo.org/record/1428464/files/article.pdf
[3] http://kielich.amu.edu.pl/Stefan_Banach/pdf/teoria-operacji-...
As mentioned in some other comment, a constant function is continuous but is obviously not what the article is about.
The important thing is that what is considered expensive is not to compute the objective function or its gradient, but to compute it over the entire dataset. Line-search would require evaluating the function (and its gradient) over the entire dataset several times, which completely defeats the purpose of stochastic gradient descent.
One could imagine doing a line search using the approximate function or its gradient (coming from the evaluation at a single data point) as the basis for a line-search, but intuitively it does not make much sense to fine-tune the step size to a single example, and this would in any case destroy the guarantees provided by the Strong Wolfe conditions.
Finally, there are convergence guarantees for stochastic gradient descent with fixed learning rate when the objective functions are convex.
> Analyzer maintains a "database" of input facts (source code + information about project structure) and derived facts (syntax trees, name resolution information, types). The client then can change input facts, and query derived facts at the current state of the world.
seems that it could also be adopted by a language sever for Rust.