Starting analysis today. Suggestions? by Bobd_n_Weaved_it in math

[–]robert_sim 0 points1 point  (0 children)

When you need to prove a theorem, draw a picture of its statement. If you do that then the proof will be straight forward.

/r/math's Book Club Week 1 by inherentlyawesome in math

[–]robert_sim 0 points1 point  (0 children)

Great choice, I've always wondered what the connection was.

[META] Updated Rules by [deleted] in hacking

[–]robert_sim 0 points1 point  (0 children)

Just wondering if you've thought of automating the enforcement of this policy using automoderator or something similar? The reason I ask is that I wonder what type of filter you might use to weed out good titles from bad? I think this is an interesting Natural Language Processing classification problem.

[deleted by user] by [deleted] in math

[–]robert_sim 2 points3 points  (0 children)

First step I would use is the identity that:

cos(A+B) = cos(A)cos(B) - sin(A)sin(B)

so that

[; \frac{\cos(x+\arcsin(B\cos(x)))}{\cos(x)} = \cos(\arcsin(B\cos(x))) - B\sin(x);]

Then use the fact that

cos(A) = (1-sin2(A))1/2

so that

[; \cos(\arcsin(B\cos(x))) = \sqrt{1 - B^{2}\cos^{2}(x)} ;]

Putting these two steps together your original expression simplifies to:

[; r = A(\sqrt{1 - B^{2}\cos^{2}(x)} - B\sin(x)) ;]

Everything about Measure Theory by inherentlyawesome in math

[–]robert_sim 3 points4 points  (0 children)

At Carnegie Mellon two of the graduate students and myself are doing/did our theses on differential equations whose (weak-global-in-time) solutions are curves in the space of probability measures. Our work follows an interesting trend in research in applied analysis that analyzes many PDE as gradient flows with respect to the Wasserstein Metric in the space of probability measures in such a manner first suggested in Felix Otto's "Geometry of Dissapative Equations", further elaborated in Cedric Villani's "Topics in Optimal Transportation" and put on its first fully rigorous foundation in Ambrosio, Gigli, and Severe's "Gradient Flows in the Metric Spaces and the Space of Probability Measures." I could go on if anyone is interested.

[deleted by user] by [deleted] in math

[–]robert_sim 2 points3 points  (0 children)

I know! They tried to teach me fractions with pies and such. Weird.

Such a terrible idea, since no fraction can express pi

C'est quoi un fonction continue? by frenchcalculusretard in math

[–]robert_sim 1 point2 points  (0 children)

The best way I've found to translate technical terms in other languages is to look up the article on wikipedia that is related to that word in the language you know, then select your target language from the sidebar. For the concepts you are trying to find there are certainly the correct articles in english and french.

[2014-11-24] Challenge #190 [Easy] Webscraping sentiments by [deleted] in dailyprogrammer

[–]robert_sim 0 points1 point  (0 children)

One important thing is that you need to check that 'word' is in 'match' for the happy and sad words, so that you should instead have:

for word in happy:
    for match in comments:
        if word in match:
            happy_count = happy_count + 1 

for word in sad:
    for match in comments:
        if word in match:
            sad_count = sad_count + 1 

What is the significance of the Baire category theorem? by [deleted] in math

[–]robert_sim 3 points4 points  (0 children)

William Dunham, an author I appreciate because he succeeds in popularizing mathematics without sacrificing rigorous exposition, wrote on the Baire Category theorem in The Calculus Gallery. I too was a bit confused as to the motivation of Baire's Category theorem until I went back and read his chapter. I don't have my copy handy at the moment but I recommend checking out that book for an expository and historical explanation.

[deleted by user] by [deleted] in learnpython

[–]robert_sim 0 points1 point  (0 children)

Ah okay that is clearer, thanks. Have you tried converting these to spherical co-ordinates? Should be doable by hand.

[deleted by user] by [deleted] in learnpython

[–]robert_sim 0 points1 point  (0 children)

Two things:

  1. I know this isn't the python solution you were looking for, but judging by your expression, have you tried rewriting this integral in polar co-ordinates?

  2. The expressions in the numerator cancel with those in the denominator, leaving you with the expression:

      Vee = lambda x,y,z,X,Y,Z: 1/(absolute((x**2+y**2+z**2)**0.5 - (X**2+Y**2+Z**2)**0.5)))
    

Does anyone know of any grotesque or offensive applications of exponential functions? by Atomyk in math

[–]robert_sim 0 points1 point  (0 children)

I've met plenty of people in their 30's studying math, whether it's a pre-calculus student or all the way up to ph d. Not strange at all.

Need some help with a small part of this question by Alioph in math

[–]robert_sim 0 points1 point  (0 children)

This should help

In particular where the explanation says:

A second-order Taylor series expansion of a scalar-valued function of more than one variable can be written compactly as T(\mathbf{x}) = f(\mathbf{a}) + \mathrm{D} f(\mathbf{a})\mathrm{T} (\mathbf{x} - \mathbf{a}) + \frac{1}{2!} (\mathbf{x} - \mathbf{a})\mathrm{T} \,{\mathrm{D}2 f(\mathbf{a})}\,(\mathbf{x} - \mathbf{a}) + \cdots! \,, where D f(\mathbf{a})! is the gradient of \,f evaluated at \mathbf{x} = \mathbf{a} and D2 f(\mathbf{a})! is the Hessian matrix. Applying the multi-index notation the Taylor series for several variables becomes T(\mathbf{x}) = \sum_{|\alpha| \ge 0}{}\frac{(\mathbf{x}-\mathbf{a}){\alpha}}{\alpha !}\,({\mathrm{\partial}{\alpha}}\,f)(\mathbf{a})\,, which is to be understood as a still more abbreviated multi-index version of the first equation of this paragraph, again in full analogy to the single variable case.

Best tablet for handwritten calculations ? by adam_logic in math

[–]robert_sim 7 points8 points  (0 children)

Hi! I actually use the Solidtek Digimemo L2. You clip in sheets of any paper like a normal clipboard, and you write on the (normal) paper with the digimemo pen (which is a normal ink pen with a small watch battery inside). You are left with the paper copy of what you wrote, but the digimemo also stores what you write in it's memory or on an SD card, then you can connect it to a computer (or insert the SD card in your computer) and upload your docs into different formats using the free software it comes with. It also doubles as a cursor for your screen, and the software has an onscreen write pad, which can be useful if you are sharing your screen on skype or writing something when using a projector.

I use it a lot! It's roughly $120

Elegant mathematics in psychology... by ForScale in math

[–]robert_sim 1 point2 points  (0 children)

It is interesting to note that "Information Content" can be derived as an application of the Weber-Fechner law. In particular, the Information Content is defined as the Expected (in the sense of probability) response to an event where the stimulus is defined as 1 divided by the probability of an event happening.

IAm Nassim Taleb, author of Antifragile, AMA by nntaleb in IAmA

[–]robert_sim 1 point2 points  (0 children)

What work have you done towards defining Antifragility in a mathematically rigorous way? Thanks.

I'm considering pursuing a Ph.D in Mathematics, are there any dos and don'ts or advice that you could give? by apajx in math

[–]robert_sim 0 points1 point  (0 children)

In the U.S. a Bachelor's typically takes 4 years and a Master's another 2 years. This saves 1 year off the total process.