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7:01 PM
@NovaliumCompany Watch 3Blue1Brown and Khan Academy
 
@EmilioPisanty Sure, everything is to be taken modulo future events
 
@NovaliumCompany I saw a neat example about that a couple days ago with RGB color space. Your basis vectors are $R$, $G$, and $B$. You can have linear combinations such as $\frac{1}{2}R + \frac{1}{2}B$ that comes out to be purple in that specific case. The span of those bases is the entire RGB space. You could also come up with something like $\textrm{span}(R, B)$ that would cover red, blue, purple, and all between.
 
Ok, 3Blue1Brown seem nice, I think I'll be fine. If I really don't understand something and I've tried hard to understand it, I will ask :)
 
Or I suppose if you wanted to change basis, you could go to CMYK space
 
@Blue mathematica output:
 
7:07 PM
@danielunderwood Unfortunately, color gamuts are actually more complicated than that :P
 
Aw man. I thought it was a neat example. I don't know too much about colors though
 
 {{0.157747 + 0.522448 I, -0.657747 - 0.0224476 I, -0.304193 - 0.168894 I, 0.195807 + 0.331106 I},
  {-0.657747 - 0.0224476 I, 0.157747 + 0.522448 I, -0.195807 - 0.331106 I,   0.304193 + 0.168894 I},
  {-0.304193 - 0.168894 I, -0.195807 - 0.331106 I, 0.157747 + 0.522448 I,   0.657747 + 0.0224476 I},
  {0.195807 + 0.331106 I, 0.304193 + 0.168894 I, 0.657747 + 0.0224476 I, 0.157747 + 0.522448 I}}
there we go
 
There are several RGB color models that map differently onto "true" color space, and it doesn't really behave as a vector space - consider what happens when you add an RGB value to itself vs. what happens when you add a vector to itself.
(The vector doubles, and it's not really clear what happens to the color, but the straightforward result of adding a color to itself is just the same color)
 
Anonymous
@Semiclassical Thanks! :) I got:
 
Anonymous
0.1577+0.5224*i -0.6577-0.0224*i -0.3042-0.1689*i 0.1958+0.3311*i
-0.6577-0.0224*i 0.1577+0.5224*i -0.1958-0.3311*i 0.3042+0.1689*i
-0.3042-0.1689*i -0.1958-0.3311*i 0.1577+0.5224*i 0.6577+0.0224*i
0.1958+0.3311*i 0.3042+0.1689*i 0.6577+0.0224*i 0.1577+0.5224*i
 
Anonymous
7:10 PM
Looks same I guess?
 
Anonymous
Checking
 
yeah, checks out for me
 
Anonymous
Ah, so this online calculator is legit: comnuan.com/cmnn01015/cmnn01015.php
 
Anonymous
Thanks a ton :D
 
Anonymous
7:12 PM
I just installed Mathematica today. Any recommendations about how to go about learning the basic programming structure? Complete noob here :)
 
@ACuriousMind Couldn't you just choose a different definition of addition? Like a vector space doesn't put any restriction on addition as long as it's defined, right?
 
Anonymous
There seem to be some documentations here
 
@danielunderwood But $v + v = 2v$ is a consequence of the axioms.
 
my advice would be to look at some examples of code
nothing sophisticated
 
In fact, it's not addition that's the problem, but I can't really tell what scalar multiplication is supposed to be for RGB colors
 
Anonymous
7:14 PM
@Semiclassical There are some demonstration projects here: demonstrations.wolfram.com/…
 
Anonymous
I'll go through them then
 
Anonymous
Thanks
 
for example, I did the calculation as such:
A = 1/4 {{15, 9, 5, -3}, {9, 15, 3, -5}, {5, 3, 15, -9}, {-3, -5, -9, 15}};
U[t_] = MatrixExp[I*A*t/16];
U[2 Pi]//FullSimplify
sigh
 
Anonymous
Ooo, saving it!
 
I can never to get it to offset like code when I want it to
You could cut out some of that, though: for instance, you could just do
 
Anonymous
7:16 PM
A = 1/4 {{15, 9, 5, -3}, {9, 15, 3, -5}, {5, 3, 15, -9}, {-3, -5, -9, 15}};
U[t_] = MatrixExp[I*A*t/16];
U[2 Pi]//FullSimplify
 
Anonymous
Four blank spaces apparently
 
MatrixExp[I*2*Pi/16*1/4*{{15, 9, 5, -3}, {9, 15, 3, -5}, {5, 3, 15, -9}, {-3, -5, -9, 15}}]//FullSimplify
yeah, I think the issue was that my first line wasn't code and I wasn't offsetting it
so apparently it's an all-or-nothing format
if you want numerical output, you can do //N at the end
 
Anonymous
Ah, yeah. You need to post code as a separate block :)
 
Anonymous
@Semiclassical Gotcha!
 
(that's basically a short-hand for N[stuff])
i.e. g//f is the same as f[g]
which is convenient if you just want to do a quick command without worrying about braces etc
not useful for a command with multiple arguments, though
 
Anonymous
7:18 PM
Right, makes sense
 
there's a few other notational things like that
mostly for pattern-matching purposes
 
@ACuriousMind could you define a space where any scalar multiplication is identified with kind of a "fundamental"? So $n(R+B) = R+B$ and similar. I don't know that that's technically a vector space anymore. And I suppose if you had $n < 1$, you can't do that identification anymore. BTW is there a mathematical object that's somewhat like a vector space, but there's an identification like this?
Really $n$ would have to be a natural number in that case
And any scalar multiplication would need a whole number subtracted until you ended up with something in $[0,1]$
 
@Semiclassical a//f[#,b]&
 
nice
yeah, that'd work
 
242
A: What are the most common pitfalls awaiting new users?

Michael E2What the @#%^&*?! do all those funny signs mean? Questions frequently arise about the meaning of the basic operators, and I hope it will prove useful to have a sort of index for them. It would be nice to have them organized by sign instead of topic, but they do not have a natural order. One can...

 
7:22 PM
but at that point I feel like it's easier to just do f[a,b]. (depends on the situation, of course)
 
I believe you've killed that analogy. Though it seems like it would be some sort of mathematical object
 
@Blue it depends on how much time you have to devote to it, but if you have any sizeable stretch then I strongly recommend this course
 
Anonymous
@EmilioPisanty Thank you very much. I was looking for something like that. I'll go through it :)
 
can i ask a dumb sci fi question
 
Anonymous
 
7:34 PM
Guys, I took a quick look at MOSFET transistors and they seem to act just like the BJT, is there even any difference?
 
@ACuriousMind was this user suspended just to keep their total vote count pretty for longer?
 
Anonymous
 
@Blue Thanks :-D
 
@EmilioPisanty That link doesn't go where you want it to go, but rest assured aesthetics rarely enters into our decision process :P
 
@ACuriousMind it goes exactly where I want it to go
thank you very much
;-)
 
7:37 PM
@Blue In a BJT will the current from base combine with the collector at the emitter?
 
oooohhh, also
I should vote 30 more times and then stop forever
 
Anonymous
@NovaliumCompany Yes
 
@Blue So I can use a transistor as an amplifier by putting a small audio signal (for example) through the base and large current through the collector, and the transistor will spit an amplified version of the audio signal?
 
they should give this guy a lurker badge
 
Anonymous
7:40 PM
@NovaliumCompany There are three possible modes of a BJT transistor. Not all modes are suitable for current amplification. Actually, I got to leave now, but you could search for "Neso Academy" lectures on BJTs (on YouTube), for the details.
 
eleventh place on all-time votes
zero questions, zero answers
just ~forty rep from suggested edits
 
@Blue Ok thanks. See you :)
 
Anonymous
This is the playlist
 
Anonymous
Okay, goodnight :)
 
Anonymous
7:47 PM
@EmilioPisanty Normal Human is/was a Math SE bot, I thought?
 
Anonymous
I remember seeing that quote: "I am a normal human typing with my human hands." before
 
Anonymous
Hmm
 
Anonymous
He's running a bot to do that. — Daniel Fischer ♦ Oct 27 '15 at 10:11
 
Anonymous
7:53 PM
Ah, so it makes sense now :P
 
11:03 PM
Ugh...not looking forward to the new site themes
 
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