933 reputation
311
bio website
location Rome, Italy
age 22
visits member for 1 year, 3 months
seen Mar 25 at 14:25

Feb
13
comment If $f,g$ are continuous at $a$, show that $h(x)=\max\{f(x),g(x)\}$ and $k(x)=\min\{f(x),g(x)\}$ are also continuous at $a$
You are welcome my friend :-)
Feb
13
answered If $f,g$ are continuous at $a$, show that $h(x)=\max\{f(x),g(x)\}$ and $k(x)=\min\{f(x),g(x)\}$ are also continuous at $a$
Feb
11
comment Question on conservative fields
@JesseMadnick if they are equivalent, why is it relevant?
Feb
10
answered directional derivatives implications
Feb
10
comment Limit of a solution of a Euler Lagrange differential equation
I thought the question was quiet interesting, let me know if I can improve it in some way, maybe provide more details about the context. Or would it be more suitable on Phys.SE ?
Feb
9
answered Conservation of Energy on Pendulum
Feb
9
asked Limit of a solution of a Euler Lagrange differential equation
Feb
3
comment Simple closed set proof
Well, I guess it really depends on (a) your taste (b) what kind of answer is requested in your assignment. What you are doing in your (correct) proof is essantially what is synthetized in lhf's answer or in mine, when I naively say that it's obvious that such sets are closed. The three ways are equivalent.
Feb
3
comment Simple closed set proof
You mean the “obviously close” statement? Well if it is for an exam, you'd better write something like “Suppose $x_1 <0$... if we take $\varepsilon >0$ very little, then... hence...” :-P
Feb
1
accepted Proof of $|\int _a ^b \mathbf f | \leq \int _a ^b |\mathbf f|$
Feb
1
accepted Definition of the Hamiltonian via Legendre transform.
Jan
30
answered Simple closed set proof
Jan
30
comment is there a nicer way to $\int e^{2x} \sin x\, dx$?
If I may add a comment, this works because integration and derivation, seen as operators on the space of functions, both send the subspace of functions of that form considered into itself. Nice solution, +1.
Jan
23
comment Way to find volume of the solid
Obviously all the edges are straight lines... right?
Jan
19
comment Solving an equation with the form $Ax=b$
Are the bottom-left entries $2,3$ wrong?
Jan
18
comment Functions That Retain Their Form When Inverted
Hi Lucian, this looks like a reasonable criterion (that the implicit form should contain some kind of symmetry), but how should “symmetrical” be interpreted? If I have an expression like $y=ax+b$, the implicit form $y-ax=b$ looks far from symmetric and yet the inverse is of the same form.
Jan
18
awarded  Yearling
Jan
18
accepted On the uniqueness of the solution given by the fixed point theorem - What is the full condition?
Jan
18
comment On the uniqueness of the solution given by the fixed point theorem - What is the full condition?
Hi Martìn, sorry but I don't understand what you mean.
Jan
18
comment On the uniqueness of the solution given by the fixed point theorem - What is the full condition?
Hi Daniel, this was my first idea. But how can you say that $|y(t)|\leq M |t|$? Applying the mean value theorem we get: $$|y(t)|=|y'(ht)||t|=|f(y(ht),t)||t|,$$ for some $0<h<1$, that we can estimate with $M$ only if we assume that $|y(ht)|<b_0$, that is more or less what we are trying to prove!