KvanteKat
Joined 6 years ago
Joined 6 years ago
There was a really interesting talk given by Mathias Shindler (long time editor of German Wikipedia) at the 39C3 conference about this topic a few months back that is worth a watch for anyone interested in the issue: https://youtu.be/fKU0V9hQMnY
- The characteristic function of a random variable X is defined as the function that maps t --> ExpectedValue[ exp( i * t * X ) ]
- Computing this expected value is the same as regarding t as a constant and integrating the function x --> exp( i * t * x) with respect to the distribution of X, i.e. if X has the density f, we compute the integral of f(x) * exp( i * t * x) with respect to x over the domain of f.
- on the other hand: computing the Fourier transform of f (here representing the density of X) and evaluating it at point t (i.e. computing (F(f))(t) if F represents the Fourier transform) is the same as fixing t and computing the integral of f(x) * exp( -i * t * x) with respect to x.
- Rearranging the integrand in the previous expression to f(x) * exp( i * -t * x), we see that it is the same as the integrand used in the characteristic function, only with a -t instead of a t.
Hope that helps :)
In my own experience teaching teaching probability theory to physicists and engineers, establishing this connection is often a good way of helping people build intuition for why characteristic functions are so useful, why they crop up everywhere in probability theory, and why we can extract so much useful information about a distribution by looking at the characteristic function (since this group of students tends to already be rather familiar with Fourier-transforms).
Despite it being a non-starter from a pragmatic standpoint, we could for instance easily imagine a novel numeral type that encodes the set S = {a + b·π where a and b are integers} (we can encode integers quite easily and all we need to reposesent such a number in silico is to encode a and b). Using such a numeral type, we are able to do exact arithmetic if our operations are restricted to addition and subtraction (and if we are content with fractional representation of numbers as being considered "exact", we can also do division and multiplication although we would have to work within the larger set S' = { (a + b·π) / (c + d·π) where, a, b, c, and d are integers and c·d ≠ 0} rather than within S).
I don't have direct evidence for my speculations, but I presume the reason [fraktur](https://en.wikipedia.org/wiki/Fraktur) was more common in mathematics back in the days is largely down to articles having to be type-set using movable type. If you insisted on using ℝ over 𝕽, you were likely to make life considerably harder for your printer (which in turn meant higher printing costs), since they would be considerably more likely to have to cast new types. As printing was modernized and movable type was replaced by more flexible printing-technologies, this pragmatic reason for preferring one glyph over the other went away. Another explanation/contributing factor is that the switch seems to have occurred in tandem with the barycenter of mathematics switching away from continental Europe and towards the US in the post-WWII period (at least if we disregard Soviet mathematics which also flourished in this period, but which was largely published in Russian). The average American would probably be less familiar with 𝕽 and other fraktur glyphs than the average German.
There are not really any known effective clinical interventions (be they in the form of medicine, therapy, or things like more exercise), and a 10% improvement is better than nothing (clinical therapy (notably Cognitive Behavioral Therapy) is generally believed to be more effective but not by that much and it is financially out of reach for many people who are able to afford medication).
The problem with talking about doing "things that will help them" is that we don't really have a lot of effective clinical interventions. Even the most common interventions (SSRIs, Congnitive Behavioral Therapy, physical exercise, etc.) are not really that effective at treating depression and have little to no effect in large parts of the affected population. That being said, these treatments _do_ work for some people so they should definitely not be dismissed out of hand (although it may in some cases be regression to the mean more than anything else, i.e. if you get better after a while on your own but have undergone treatments of one form or another you may erroneously believe your most recent treatment was effective).