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3:00 PM
Maybe they mean "|O|". :P
 
@anak I couldn't make it either
:?)
 
Is there any context to this problem? Is it for a particular class?
 
@anak yeah, this is an undergraduate level problem which I found in a handout. The source is unknown to me
 
In order to solve it, though: I would typically advise to look where the square root is undefined (i.e. where $x+6 < 0$).
 
It was given in a random problem set....
 
3:02 PM
If you are looking for real solutions only, then $x+6\geq 0$ is necessary, so you know that $x \geq -6$.
 
@anak yeah...
 
Then you do sort of what you did, you square both sides.
 
@anak But we could do it, if both the sides of the inequality were positive. That's why I took the assumption that $x\geq 0$.
 
Wait, why did you "fix" C? It was the correct answer in your previous question?
 
@AMDG (sorry for late response) thanks for being so conisiderate!
 
3:12 PM
Of course
@shintuku Yes. For sure, though, the privation of those essences do not exist as essences--that would be a metaphysical contradiction, and a thing is possible only if it has no metaphysical contradiction--but rather by necessity can only exist as ideas within the mind of creatures.
These things are called logical beings to distinguish them from actual begins (things that are essences, or which have essences).
For example, nothingness isn't a thing that has real existence per se. By definition, nothingness is the privation of being, so if nothingness did exist, it would both exist and not exist, therefore the essence nothingness doesn't exist, only the idea of nothingness.
Nevertheless, it is objectively so that as a concept or notion, it exists, and thus excuses it from being merely called the invention of man.
Privation of being in itself is not contrary to existence; nothingness is the absolute privation of all being.
 
@Franklin And yes, you are right, but then when you got to your inequality with the factored parts, how did you conclude that $-2\leq x\leq 3$ if you prior assumed that $x\geq 0$?
 
Ok, but why does truth need to be involved in the actual possibility or impossibility of things? This seems to me more like truth about reality or being, i.e. an added judgement, a proposition, about possibility or impossibility @AMDG
I'm not seeing again why truth is being distinguished from true knowledge
Why is it that truth consists of two species, possibility and impossibility, instead of being about two ways of being, possibility and impossibility?
 
@anak ok, ok, ok,....Let me clear it by saying: A. $-3\leq x\leq 3$, B. A circle and a pair of straight lines C. -2<=x<=3, D. $-6\leq x\leq 3$ . These are the options given. Actually, while copy-pasting, the options part gets mixed up....
 
"that which is possible" and "that which is impossible" seem to me to be propositions, so I don't see where truth is beyond the judgment by a brain that things are so
 
@shintuku Well you basically demonstrate it in what you just said. Impossibility and being are wholly contradictory. I recognize this non-conformity of impossibility and being, and this recognition is a conformity of that which is in my mind, and that which is in reality.
@shintuku Propositions are just propositions. There is something in them which of their essence is true or false.
 
3:20 PM
@Franklin Okay, now the correct answer is there. :P
 
@anak Umm...Here, I will say, that $-2\leq x\leq 3$ is the solution set for this inequality: $x^2-x-6<0$ and not for the inequality $\sqrt{x+6}\geq x$. The solution set of the given inequality is actually, a subset of the solution set of this $x^2-x-6<0$ under the assumption $x\geq 0$
@anak but how to prove it ?
 
Sure, let this recognition be a conformity of that which is in my mind, and that which is in reality. Why is there immateriality involved here?
 
How do you think anyone judges? That judgement must be coming from somewhere. Something must be compared against. What is it that man is comparing against? None other than truth: the idea is compared with what is true, and the pronouncement of that idea's conformity or non-conformity is a judgement.
 
but why is it immaterial, i don't see why it has to be immaterial
 
@anak Do you suggest the hit and trial way as generally done in case of mcqs ?
 
3:22 PM
@Franklin Well that's my question. You concluded $-2\leq x\leq 3$, after assuming $x\geq 0$. So really at most you could say is that $0\leq x \leq 3$.
 
@shintuku What is material to you?
 
This question you do not need to do testing to solve. You can fully justify your answer without knowing the final answers.
 
@anak your last statement in this comment is correct.
@anak how ?
That's my question...
 
@AMDG composite of atoms or strings or whatever
 
@Franklin Well are you confident in how you conclude that it works for $0\leq x\leq 3$?
 
3:24 PM
@anak yes, sure!
 
@Franklin And you are confident in how you conclude that it doesn't work for $x\leq -6$?
 
@shintuku So what is not clear about something immaterial being something not composed of atoms, strings, etc.?
Can you compose an idea even out of atoms?
 
@anak you mean $x<-6$ , right ? If so, yes....
 
Can you create knowledge out of clay?
No, therefore it is immaterial.
 
@Franklin Yes, sorry, I got \eq happy.
So what $x$'s remain to be checked?
 
3:26 PM
@anak [-6,0) ?
 
Great, so try assuming this and look at the inequality: what do you notice?
 
@AMDG no but these are phenomena which are produced by the brain. you were arguing that these must appear beyond the brain, in the intellect or spirit, otherwise reality ceases. i don't understand why
 
Well because as we've defined truth, if something is impossible, it cannot exist. The possibility of an object existing must first exist before the object itself can exist.
That possibility is what belongs to truth.
Or impossibility of course
 
yes, the knowledge of impossibility/possibility, i.e., true knowledge, no?
or what do you mean by 'belong to truth'
 
There is possibility and impossibility, and there is my awareness of that fact which is knowledge.
 
3:30 PM
ok, i follow you
 
@anak ohh... I solved it like this: if $-6\leq x\leq 0$ then, $0\leq x+6\leq 6$ and thus , $0\leq \sqrt{x+6}\leq \sqrt 6\leq 6$. On the other hand, $-6\leq x\leq 0.$ Comparing the range of $\sqrt{x+6}$ and $x$ the given inequality becomes obvious , right ?
 
Epic
 
so, there is possibility and impossibility, and there is my awareness of that fact which is knowledge
so where are we with truth?
why is truth distinct from true knowledge?
 
Ok, so what are you meaning by true knowledge?
 
@Franklin You have convoluted it a bit, but that's the idea. Really just look at the sign on both sides. On the left, it's $\geq 0$, while on the right it's negative.
 
3:34 PM
@AMDG false knowledge would be, e.g., believing we know that the sun orbits the sun. true knowledge is knowing it is the opposite way around
 
@anak yes, that's it! Thank you!
 
@shintuku That conformity itself as opposed to your having the awareness. You are quite literally stating the species of knowledge (which necessarily correspond with the species of truth) as knowledge of what is true, and knowledge of what is false (your wording there is ambiguous).
 
alright, but that's a material process. the conformity is a physical state in the world
why would it be immaterial?
there's my subjective evaluation and there's reality, and they conform.
if truth is nothing but this conformity, why are we positing it is immaterial?
 
Physical state is not a material being. Conformity is not a material being. There's where your error lies.
 
how so
 
3:39 PM
Those are recognitions, in the simplest sense, of some physical reality.
 
sure, in the brain
 
That recognition is distinct from the reality being recognized. Electrons flowing in the brain are not knowledge in themselves anymoreso than data is not information.
 
it's not the electrons, it is the machinery of the brain that produces knowledge
so why would conformity not be a physical state?
 
Conformity can be a physical state, but neither of these are material things in themselves because they're ideas.
Where is the machinery of the brain getting that knowledge if the brain produces the knowledge?
 
sure, but ideas are products of the brain. the brain analyzes sense-data to produce knowledge
 
3:45 PM
Ok, I think I see what you're saying now.
 
conformity, if it is the same as truth, then, isn't anything else than an idea, which is a product of the brain
otherwise, it is a physical state between the brain and reality
why would we at any point need to posit immateriality, for fear of losing reality?
 
Now that is all well and good to claim, but the brain is insufficient to explain why we have understanding of an idea, and why we can go up and down a hierarchy of ideas, and why these ideas are the same for everyone who has their knowledge.
 
how so? it seems to me that sufficiently complex computations could produce all the things you've just mentioned
 
They can, but who is the mover?
The brain is a horse and the spirit is the rider.
 
i don't understand, why are you asking who is the mover?
to posit something immaterial? why would it need to be immaterial?
why is the mover not in the brain?
 
3:49 PM
Why does a horse not steer itself?
 
it can before it is tamed
 
Nothing causes itself.
 
otherwise, it will if it is sufficiently hungry
 
Where does hunger come from? Why does it have that impulse? Did the horse put those there?
 
its a series of neural transmissions from its body
the horse's brain, as an artifact in its neural network, receives those impulses and processes them
 
3:51 PM
Is the horse capable of contradicting those or not?
Does it even understand any of the concepts we're discussing?
 
from fear, maybe, or if it senses danger is involved if it tries to feed at a particular source. otherwise animals tend to follow their instincts.
but it can be conflicted, e.g., if asked to cross water by its rider, and it is scared of water
i'm not sure i get how this is related to the mover and brain stuff, but that's how i understand the workings of horses
horse theory, if you will
 
That would be a decision, but if it's merely a brain which chose it, then we must be obliged to say that the horse's actions have a specification of action and chronology which is software. Anything that operates according to it will never deviate. If that's true of humans, then we should observe within ourselves an incapacity to resist hunger, or any impulse at all, yet you can disregard it for arbitrary reason, therefore there must be a cause greater than the brain itself.
 
i don't see how any of that follows. why can't the horse be conflicted over whether to feed somewhere because it's scared of wolves
and why would we be incapable of resisting hunger if our brains were similar to a horse's
if it is just a horse's brain but more complex, maybe we simply have a better ability to postpone satisfaction
we also know we tend to be unable to resist impulses when our prefrontal cortex is destroyed
 
Why is it scared of wolves? You don't see any necessity for truth to be immaterial, or even that there has to be any immaterial agent whatsoever, yet neurons are, if wholly material, dictated by the laws of physical reality, and the motion of atoms, and in spite of the stochastic or random nature, order somehow proceeds from it deterministically, so that means that given sufficient memory and resources, a brain can be fully simulated.
If something is deterministic, it necessarily proceeds from necessary being and will simply execute and do nothing but its programming.
 
we see our typically human abilities become seriously compromised when we suffer injury to specific areas of the brain
we could simulate our brain, yeah
we don't have the capabilities yet
 
4:01 PM
Can anyone please help me understand how are they getting the equation: $(x(k+1)-kx_0)^2+(y(k+1)-ky_0)^2=r^2$ in this question : math.stackexchange.com/questions/3193174/… ?
 
enough damage to the brain, and we can even wonder whether someone possesses consciousness anymore
 
@shintuku Ok, then it should produce repeatable results, but in reality, I as a human am capable of contradicting any such simulation of my brain as it exists right now, therefore there must exist some cause greater than the brain, therefore greater than atoms, and therefore greater than material being according to your definition of material being.
 
I am talking about the post by the answerer
 
@AMDG sure, you can contradict it if, for instance, that simulation is not aware of you, but you, to spite it, or to spite the scientists, decide you will do something otherwise. no need to follow the rest of your chain of consequences
 
@AMDG depends a bit on what we mean by deterministic. Suppose you have a system which is entirely governed by a sequence of inputs. Then that sequence determines the outputs, so formally it’s deterministic. But if the inputs are essentially random, then that determinism doesn’t really help you predict anytging
 
4:04 PM
nothing in all of this gives me even an intuition about why we're positing immateriality of truth, or of anything at all
i don't understand why its materiality has catastrophic consequences
 
@shintuku What, the fact that if truth were material, i.e., constructible of material being per your definition, it would mean that the truth only exists for as long as the object exists, or we exist?
 
Philosophically it’s an interesting question whether the brain itself is deterministic, but as a practical matter the inputs to the brain are certainly stochastic.
 
@shintuku Even though we already established that objects are not contingent on our minds (which are material beings according to you)?
 
@AMDG no that part is fairly understandable, that's just true knowledge. if no one knows something, then, well, that knowledge disappears from reality. i don't get why you're positing that you need immateriality otherwise reality itself disappears
yes we established objects are not contingent on our minds
 
To my previous comment: I got it now. A good answer though. Thank you!
 
4:08 PM
Statements about objects can be contingent tho
 
yeah
 
@shintuku Because knowledge or truth can't disappear from reality. If we agree that possibility and impossibility are true knowledge, then your statement reduces to the absurdity that truth is contingent on the mind of man, i.e., possibility or impossibility themselves are contingent on the mind of man and his knowledge of them, ...
 
why? why, if truth is contingent on the mind of man, possibility and impossibility themselves become contingent on the mind?
 
...but you're saying that if no one knows something, then that knowledge disappears from reality, but that would have to mean that the possibility or impossibility must cease also, but the object having possibility itself needs to be capable of existing by definition of possibility, so it would have to cease existing, therefore truth is immaterial.
 
no, why would the possibility and impossibility cease also??
 
4:12 PM
Because you said "if no one knows something, then, well, that knowledge disappears from reality."
 
yes
if no one knows something is possible, why would it become impossible?
or cease to exist?
 
So if the knowledge of possibility and impossibility cease to exist, then you must also claim that either possibility and impossibility cease to exist, or that they continue to exist despite our not knowing them to exist, and therefore must admit that truth is an immaterial being.
 
why? why the last case?
i don't get this, this is what I don't understand. let them continue to exist without any knowers. why is there immaterial truth?
 
Because it is the only possibility. These exhaust the options.
 
how? why is that a logical consequence?
there's the other possibility: they continue to exist without any knowers
 
4:15 PM
Because there can be absence of knowers, and absence of the objects themselves.
Both are material per your definition
 
right, both are material, but I'm not seeing that truth is an immaterial being, why are you drawing this consequence?
let them continue to exist despite our not knowing them to exist, why must i therefore conclude truth is an immaterial being?
 
The better question is why aren't you drawing this consequence? If a material being is made of atoms, etc., then it is a material being; if not, then it is an immaterial being by definition.
 
yes I agree
but why am i drawing the consequence that truth is not made up of any atoms, in someone's brain?
 
Ok, so then if I understand correctly, then the question that you need to answer is: what are possibility and impossibility apart from the knowledge of possibility and impossibility?
 
no, i know that those things are different
 
4:18 PM
Right, but what are they?
 
they're very distinct things, one pertains to reality, the other to the mind
possibility and impossibility are properties of a physical state, while knowledge of them are states of mind
 
Not so. Atoms are possible. This is self-evident from the fact that they exist, and their existence is empirically proven, even if their constituents are still a matter of reasonable belief.
How then can it be said that this is simply a property of an atom's physical state?
 
are you saying that atoms are possible in the sense they could be constituents of physical reality?
 
I'm saying atoms are possible in that they exist. If they didn't exist in reality, then we could only say they may or may not exist.
If a thing exists, it is possible, and the converse is also true.
should say if a thing can exist, it is possible, and the converse is also true
 
right, so what's the problem with atoms? that they are possible is a judgment of the mind
if they are in fact possible is an affair of reality
where's the issue?
 
4:23 PM
Ok, so let me ask you this: is reality made of material being to you?
Is reality identical with material being?
 
physical reality, as distinct from, say, emotional reality, or imaginary reality. yes, physical reality is made of material being
 
Follow-up: what kind of being is a state to you?
 
i don't understand
 
What about a property?
 
a physical state?
or what sort of state
 
4:25 PM
State is state. What kind of being has it?
 
we may speak of a physical state, an emotional state, the state of affairs, etc., or designate the word, or its idea
do you ask about a physical state? it is a configuration in space of atoms
 
You've mentioned two kinds of state, so I suppose you could start with telling me what you say is the kind of being that physical state and state of mind have.
What is a configuration in space?
 
say I have a room, the bed is in the north corner. i will change the configuration in space of the bed and the room if I move it south
I may also change the rooms configuration in space if I had a machine that could lift it up, the entire room
or balloons, like in Up!
 
Great. Is that configuration itself material or what other kinds of being do you think configuration could be?
Could it be immaterial perhaps?
 
yes, a configuration of space could be immaterial in the sense it would be, for example, in a dream of mine
 
4:28 PM
Can I construct a configuration out of atoms itself? I don't think so. I can't construct a number out of atoms either.
 
then I could make an imaginary configuration of space of my room
i use such configurations of space to memorize things using a technique called memory palaces, to remember quotes, historical dates, etc.; in my mind i can make things arbitrarily far away from one another
 
Great. So do we agree that immaterial means not made of atoms, etc., nothing more nor less?
 
why can you not construct a configuration of atoms in space? certainly CERN seems to do so, isolating certain types of micro particles
 
I'm not asking if you can construct a configuration of atoms. That would be asking me to arrange atoms in a certain way. I'm asking if you can construct a configuration itself of atoms which is not to be found in the atoms themselves.
Atoms are just there, existing in space. They don't relate one to another. The configuration is a recognition of their relations in space.
Can I construct a recognition of a material being using a material being?
 
do you mean if I can construct the word itself, or the idea itself, with atoms? no, those aren't the type of things you can do with atoms. the word maybe, as it is the collision of air atoms in a particular way, but the idea can be constructed from atoms through a brain
 
4:32 PM
why is the cross product also $||a||||b||\sin\theta$
like why both definitions
 
if you can construct the recognition of a material being using a material being: image processing AI seem to be there
 
guys, the FCC says you can't go this long without a station id. you're listening to Bongrip Universe on KUSH 101.3. the time is 9:33.
 
lol
 
@Obliv it's the value of the modulus
 
@shintuku So your claim is that ideas are constructed from atoms through a brain? I see. So your claim is then equivalent to saying that ideas are arrangements of electrical impulses? Is that correct?
In other words, do you believe that a series of abstract concepts which are not literally equal to electrical impulses are in fact just electrical impulses literally?
 
4:35 PM
yeah, or electrical impulses in the brain, with neurons, arranged in a particular way
 
$A = \begin{bmatrix} a_1 \\ a_2 \\ a_3 \end{bmatrix} B = \begin{bmatrix} b_1 \\ b_2 \\ b_3 \end{bmatrix}$
 
@AMDG they are equal in the sense that they can be recognized as a configuration inside the brain, or as the organization of the brain at a particular moment, yes
 
@SineoftheTime given these two column vectors (the inner product & vector product don't apply to m by n matrices in general or do they?
 
@shintuku Ah, I see, and how might one recognize a configuration which is immaterial? An immaterial cause such as a spirit perhaps?
 
I guess I'll just do it brb
 
4:37 PM
I mean all things considered, surely you don't believe that an electrical impulse along a wire is literally, e.g., the essence of the set of all reals for instance?
 
@AMDG i don't understand this, is this a rhethorical question?
 
Rather, that the idea must exist accidentally within it? That the arrangement or configuration of those impulses, of which each has no meaning in itself, is something subject to an interpretation?
 
@AMDG an interpretation is something done by a brain, reduced to a physical state it is also the result of neural activity
i don't get this line of questioning
did you rhetorically conclude to an immaterial spirit, if so, why. i didn't understand
 
@Obliv It’s not!
 
@shintuku Literally reductio ad absurdam: the electrical impulses cannot themselves be the concepts or ideas themselves, nor can their arrangements in themselves constitute the ideas. They must be subjective representations... of something greater than themselves.
Because these things in themselves... only mean what they are in themselves.
 
4:41 PM
no the electrical impulses are not the ideas themselves
 
An arrangement is merely an arrangement.
An electrical impulse is merely an electrical impulse.
 
yeah
 
nvm inner product seems to make sense for large $m \times n$ matrices doesn't have to just be column matrices
 
in the processes with which the brain is occupied, it becomes an idea
 
@TedShifrin this book uses the notation $\alpha''$ for a curve $\alpha$ on a Riemannian manifold to mean $\nabla_{\dot\alpha}\dot\alpha$. Is this pretty standard?
 
this is the 100th reductio ad absurdam you make that I have no clue how it came about
these don't follow
 
@TedShifrin in general is $A\cdot B = a_{11}b_{11} + a_{12}b_{12} + ... a_{1n}b_{1n} + ... a_{m1}b_{m1} + ... a_{mn}b_{mn}$
 
Quite frankly, I don't see what's so hard to see. We've just acknowledged that the idea is not the electrical impulses. Ok. So what is an idea, then? What is it made of? is it material or immaterial? If material, then the only thing it can be is electrical impulses and their arrangement, but obviously, neither of these tells of themselves, e.g., the numbers, or life and death, or existence and being, etc.
 
if the size of the matrices aren't equal you just increase the size of the smaller one and fill in 0 for the entries?
 
So we are forced to conclude that an idea is immaterial, and if immaterial, then the things which ideas either are or represent must also be immaterial.
 
4:47 PM
not sure if the cross product has a generalized form in spaces larger than $\mathbb{R}^3$
(or smaller)
 
therefore truth, configuration of atoms, etc. are immaterial (and indeed, a configuration is a logical being).
 
@AMDG the idea is a configuration of electrical impulses in the brain, understood physically. understood phenomenologically from a point of view within a subject, it is, e.g., what I experience happening when I do 2 +2 in my subjective experience
the subjective experience has a material manifestation in brain activity
 
@shintuku Configurations are not physical. They are relationships. Relationships are not material beings.
 
Maybe you guys should create another room for this conversation...
 
^
 
4:50 PM
@anak Yes. Also standard is $D/dt$ instead of $d/dt$.
 
Fair
 
@Obliv You can define a dot product on $m\times n$ matrices by taking the trace of $A^\top B$.
Cross product only defined in $\Bbb R^3$, but it is a vector. So your formula I tagged gives only its magnitude, not the answer.
 
Right, I just wasn't sure why the magnitude was defined in that way
 
It is usually a consequence of the definition, not a definition.
 
Thanks Ted!
 
4:54 PM
There's a 7th dimensional cross-product, kind of. en.wikipedia.org/wiki/Seven-dimensional_cross_product
 
welp matrix multiplication doesn't serve as the definition since it doesn't even work in $\mathbb{R}^3$ since the sizes are off
unless you did the transpose of one, but you'd then have a 3x3 matrix..
I see the problem, you can't get the determinant of a non square matrix.
not sure if this has any merit but defining a cross product in higher dimensions would require more vectors so $\mathbb{R}^n$ only works with $n-1$ vectors
but what $A \times B \times C$ in $\mathbb{R}^4$ means I do not know
$\begin{bmatrix} i & j & k & l \\ a_1 & a_2 & a_3 & a_4 \\ b_1 & b_2 & b_3 & b_4 \\ c_1 & c_2 & c_3 & c_4 \end{bmatrix}$
oh
it just produces an orthogonal vector in $\mathbb{R}^4$ ?
 
5:16 PM
@Obliv Indeed. I have a section in this answer that talks about this.
"Finding A Perpendicular Vector"
 
Ah yes
With the unknown vector being the i,j,k,l
 
The $i,j,k,l$ are the $4$ basis vectors
$a,b,c$ are the coefficients for three vectors
the determinant is the vector perpendicular to all three.
 
 
2 hours later…
6:53 PM
Is there some geometric idea for $\kappa = \frac{|T'(t)|}{|r'(t)|} = \frac{|r'(t)\times r''(t)|}{|r'(t)|^3}$
like the magnitude of the binormal vector divided by the magnitude of the tangent to the 3rd power..
nvm $B = T \times N = \frac{r'(t)}{|r'(t)|} \times \frac{r''(t)}{|r''(t)|}$
well $|T'(t)| = 1$ so really it's a unit vector along the normal to the curve at any given point divided by the magnitude of the change in slope
so the ratio of how much the curve is changing w.r.t. the normal
Not sure why it's not just $\frac{1}{|r'(t)|}$
 
well, that wouldn't even work for circles, would it? so it's got to be something else. i don't have intuition for the non-unit-speed formulas.
i just think of them as 'the complicated thing that you get if you don't have a unit speed parametrization'
the formula (whatever it is) should be invariant under changing r(t) to r(kt), k nonzero constant. that rules out a lot of candidates (including that one). it should also scale inversely with changing r(t) to k r(t) (which your candidate formula does do). i don't think scaling alone clearly immediately spits out the right formula, though.
 
 
2 hours later…
8:41 PM
@Jakobian I know nothing about p-adic numbers, sorry
 
 
1 hour later…
9:43 PM
so, $\infty^0$ is listed as an indeterminate form. is $(-\infty)^0$ an indeterminate form?
 
Funny guy you....when would one of all those sorts of combinations every be anything but an indeterminate form?....It may be the case, but I'm just going off of all the beginner's calc....
 
because there are some examples of changing the sign of infinity in an indeterminate form that makes it determinate
 
shin: what would that mean? OK, you have a function f(x) going to -infinity, and a function g(x) going to 0. but what would f(x)^g(x) mean in that case? what is (-1)^(1/2) for example.
 
real exponentiation with a negative base is subtle
 
9:47 PM
oh, it becomes complex
argh, how do I even think of $(-1)^x$
am trying to graph $x^y = z$ for some intuition here
 
Ted why did you never write a Real Analysis book?
 
Never even taught the course officially.
 
By choice you never taught it?
 
Yup.
 
Why? Just curious since all you teach is the progression to that advanced material
 
9:57 PM
Plenty of analysis in the Spivak and multivariable math classes, which I taught something like 14 times each.
 
Plus your book/teaching is very comprehensive
Don't disagree...I guess in a sense your courses are a very good preparation for those analysis courses
 
wolframalpha failing me, so is desmos. onwards to excel!!
 
10:20 PM
would I be wrong if i said, it seems that $f(x)^{g(x)}$, with $f(x) \to -\infty$ and $g(x) \to 0$, tends to $0$?
both the imaginary and real parts seem to keep getting smaller
not the case for $\sqrt[x]{x}$
 
10:44 PM
any chatgpt bots in here?
 
@shintuku that is indeed wrong
 
yeah i'm seeing the real part going to 1 instead
 
First of all, with $f\lt0$, the exponential may not be real, or possibly ill-defined.
 
how come it could be ill-defined?
 
What is $(-1)^{.47}$?
 
10:55 PM
hm that's bothersome, all I know how to deal with are exponents of the form $1/x$
oh wait: $\sqrt[100]{(-1)^{47}}$?
 
Then $(-1)^{1/2}$ is not real
 
@copper.hat How is life back in the rat race?
 
right robjohn, that much I know
 
When the exponent is not an integer, the exponential is well-defined for positive reals (by convention), but for negative reals, it is not so nice.
 
it could be complex, but why could it be ill-defined?
 
10:58 PM
shin you're basically wrestling with defining the complex exponential. you can do that, but it does not have all of the nice properties of the real exponential. why are you doing this? are you just trying to assign meanings to expressions?
 
i'm trying to figure out if $-\infty^0$ is an indeterminate form, i.e., if two functions that go to $-\infty$ and $0$ might make something not nice happen
 
@D.C.theIII just working my way back in slowly. i flew to Rome for a nephew's wedding and them spent a day in Dublin with my 94 yo aunt. very nice, but i am too old for this sort of travel
 
@shintuku ill-defined because the logarithm is multi-valued.
 
oh i see
 
plus i picked up a stupid cold. next time i will try for a smart cold. all the rage.
 
11:00 PM
@copper.hat you can access them on the web
 
Never too old for travel.........you're just too old to deal with all of TSA's nonsense
 
normally when people talk about indeterminate forms in calculus, they mean that the value of one real-variable limit cannot be determined from other real-variable limits. the "0^0" stuff is shorthand for statements about limits. here, we're saying, you don't even have real-variable limits.
 
:-) cloud colds?
 
hm right leslie
 
the comparison between Bart & the trains ins Rome does not bear repeating
 
11:01 PM
and before you discuss limits of a^b where things might be complex, you need to discuss complex numbers in general, i.e. what that means before you take any limit. the base a being real isn't much of a simplification here - once a is negative, you're in complex land and have to consider the whole nightmare realm of complex numbers.
 
right that makes sense
 
the properties of the complex exponential are subtle and not as nice as the real exponential. that restriction to positive real bases in real analysis books is a very meaningful one. even for rational exponents.
 
SOunds like it is time for you to work through Ahlfors Shin...lol
 
Actually, even for $a\gt0$ there can be a problem. It’s just that we use real logs by convention.
 
e.g. your calculator can probably take a stab at what (-1)^(1/3) is, and then square the result. and it's probably not going to be the same as what your calculator will spit out if you ask for (-1)^2 = 1 and then take the cube root of that. so a^(2/3) for negative a is subtle.
 
11:04 PM
you'd typically deal with this in a first class on complex analysis right?
 
yes, often fairly early.
 
alright noted, will defer this stuff for a while
 
you need a complex logarithm pretty early on.
 
thanks leslie and robjohn
 
@D.C.theIII i made the mistake of paying for, and going through the interview process for a global entry card. complete waste of time for me. my preferred airline does not participate in tsa precheck, so no savings on this end. on my return, used the global entry station, but it was slower than the normal immigration line. so, more more experiment.
i like conway's treatment of complex analysis.
 
11:09 PM
I'll have to take note of Conway's text for future reference. I was more saying Ahlfors in jest because I know it is complicated, from what I've read
Normal immigration for US citizens entering the US is pretty fast, it is nightmare when you're not though. It's why I try to avoid the US on my international travels
 
i have an eu passport as well, so the actual immigration part between us/eu is faily quick usually
 
Why does US immigration hate Canada so much....sigh
 
It’s Canada who won’t allow US peoples in now, isn’t it?
 
I think both borders are still requiring vax status until April
 
Copper, when I came back from Europe (pre covid) I got through global entry in mere minutes.
P.S. Welcome home.
@D.C.theIII To wit
 
11:27 PM
@TedShifrin Thanks! i was following two ladies, quite by accident, of course. One had global entry, the other didn't. The other won the immigration race.
 
I wasn't sure if you were talking about the migrant issue in QUebec or just in general
 
I wasn’t sure, but I am pretty sure that if the next election goes badly, billions of US citizens may try to become Canadian, and Canada wants no part of any of it.
 
I suppose I should read the article, but I'm not sure how that will play out in real time, there are plenty of places where people can cross if they are eager enough.
We could ship the Texans to Alberta, they would fit in there
But then again they'll be happy in the good ol US of A if DeSantis wins........( I would laugh, but we all know what happened before..)
 
please let there be more choices
 
11:45 PM
@TedShifrin Hello Ted
I have question about ODE
about the number of solutions being equal to the degree in the case of constant coefficients
 
Number of linearly independent solutions.
 
yes exactly
but if we have solutions to the char equations
such that each solution comes with multiplicity k
we do get 2k lin indep solutions
this comes from the solution and its conjugate
so why the answer is just n = degree of the DE , that many solutions
 
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