Buddy of mine finished his ls3 swapped s30 260z finished and took it to the track, this is him against a GTR. Also has a bit of bottle action going on

https://www.instagram.com/p/BoXWqy1A3Qq/?taken-by=dcr.david

Some progress shots/vids in his instagram as well. I told him i think he should have done some youtube videos, but maybe in the future!

submitted by /u/Enrager
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Question about what happens after building a model re: company profit

Say I did linear regression and got the coefficients to show that a 1 dollar increase in R&D expenditure provides a $0.5 increase in revenue. All the residuals and normality etc are looking good, so I go to my boss with the great news, and they ask me “So then how much should we invest in R&D?”. There might be a nice correlation, but it won’t hold forever, and eventually a 1 dollar increase in R&D will lead to a reduction in profit. How would you go about determining how much to invest in R&D? Using calculus to find a maximum springs to mind, but what formula am I working with? The equation for a straight line? In which case after taking the first derivative I’d be left with just the coefficient, which is next to nothing, and the second derivative would be 0 so it’s a saddle point, so quite sure that’s not the way to go. Sorry if I’m not asking this in the right place, honestly not too sure where to ask this. Am quite open to suggestions to that as well. submitted by /u/altec4 [link] [comments]

Learning the time dependant bias of a coin

I have a weird model that I am sure someone has examined before.

The bias of my coin p(t) changes in time.

Call heads ‘1’ and tails ‘0’ and the result R in {0,1}. The Bernoulli distribution is

Pr( R|p(t) ) = [ p(t) ] ^ R [ 1 – p(t)] ^(1-R)

Assume I am sampling the coin at a rate that is sufficient for my purposes.

Question: how do I estimate p(t) in a principled way?

E.g. I could try to do MaxLik on a moving window consisting of a fixed number of coin flips. But how do I choose the window in a sensible way?

submitted by /u/short_finger
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Gone back to school for math?

This is strange, but I might want to return to college later and take some math courses as part of a graduate program (which is not math itself, of course. I can’t do that. I mean something like data science or business where math is useful). I think I know now how to master math courses, a skill I lacked when took Calc 2. Has anyone gone back to school for a masters, but took undergrad math courses as part of it?

submitted by /u/1883456
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Where to drive a Lexus lfa?

I have had been to many of the rental exotic cars places and have driven many exotics (huracans, 488 etc.) I however have never been able to find any place that has a Lexus lfa. The lfa has always been my dream car and I want to drive it at some point in my life. What do you guys think would be a great way to get my hands on a lfa for atleast an hour, maybe a day? I could probably only spend up to $700 on the experience. So any suggestions or ideas?

submitted by /u/ChaosBlaze9
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Explanation of Statistic formula

I have many questions 🙁 Thanks in advance! 1. what are the differences between these two equations? y= xβ+ɛ and ŷ= xβ^ , r = y-ŷ

  1. I know that ŷ= xβ^ is the estimate equation, but isn’t y= xβ+ ɛ also the estimate equation?

  2. Assuming ɛ~N(0, σ² I_n), why is y~N(Xβ,σ² I_n) ? Shouldn’t it be y~N(Xβ+0, 1+σ² I_n) ?

  3. r =y-ŷ , which is ~N(0, σ²(I-X(XTX)-1 XT), but somehow it can become (I-X(XTX)-1XT)Y? (from my lecture note)

  4. why is the rank for r equal to (n-p-1) , but SS_tot is (n-1) and SS_exp is (p) ? How is the dimension being decide?

  5. What is SS_res/σ² used to calculate, and why does it follow a chi-sqare distribution ?

submitted by /u/MathAvenger
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