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May
25
comment Rewrite trigonometric expression to be be numerically “stable”
Yes, I would prefer a formula which is exact and which is defined at x=0. But maybe such a formula does not exist...
May
25
comment Rewrite trigonometric expression to be be numerically “stable”
Yes, this is nice! However I need to apply this formula also for "non small" values of $x$. I think I could use $x/3$ when $|x| < 0.01$ and the exact formula elsewhere...
May
25
comment Rewrite trigonometric expression to be be numerically “stable”
Yes, I could use Taylor series, but I should distinguish the case when x is not small... that I would like to avoid.
May
2
comment About Banach Spaces And Absolute Convergence Of Series
You are right! I have corrected it....
Apr
8
comment Riddle: 1 question to know if the number is 1, 2 or 3
Since the girl knows EVERYTHING about number 1, she knows if the boy is thinking to that number...
Feb
18
comment Uniform convergence and bounded increasing function.
Take the functions $f_n(x) = |\sin n| x$. These are increasing functions which do not converge as $n\to \infty$.
Feb
7
comment Question about non conservative vector field
They don't speak at all... so they are not conversative
Feb
3
comment Is $f(x,y)$ differentiable at the origin?
What is $f'(0,a)$ when $a$ is a vector?
Jan
29
comment Probability of woman receiving positive mammogram and having cancer
@AndréNicolas I think that the OP is exchanging the two sets in the definition of $P(A|B)$.
Jan
18
comment Attempt to proof the Cantor-Bernstein theorem
What you write makes little sense... $f_M^{-1}(N) = M$. Maybe you mean $f_M(M)$? You should correct your question...
Jan
10
comment Is $0$ a natural number?
@AsafKaragila I agree.
Jan
9
comment Is $0$ a natural number?
@AsafKaragila I agree with you. But I think (please confirm) that in every country a child is taught to attach numbers to things (i.e. counting) starting from 1. I think that also mathematicians do that: Problem #1 is the first problem in the list. In my experience only computer scientists do count from zero and only when talking with computers or other computer scientists...
Dec
27
comment Prove that limit inferior is same as limit superior for a convergent sequence
I've corrected it. I was sure my translation from italian was not good...
Dec
26
comment Differential geometry problem about curves
I think it is the plane containing the tangent vector and the curvature vector.
Dec
26
comment If $f'(z_0)\neq 0$ then $f$ is one to one on some open disk $D_r(z_0)$
$\varphi(z) = g(z,z_0)$ in @Donald_Edwards answer. In fact in his answer you find $f(z)\neq f(z_0)$ and you should complete the reasoning by also varying $z_0$... which is not completely trivial.
Dec
13
comment Hypothetical contradiction to Bolzano-Weierstrass
This works with every number, it is not required that the number is irrational. The digits can be 0... so some digit will repeat infinitely many times.
Dec
1
comment find the slope and intercepts of the line
The same method applies to b). You need to solve for $y$.
Dec
1
comment How to simplify / combine function equtions containing `if`?
There is not a unique way to simplify a function. For most purpouses the expression you have is the best way to express the function. Why you need a simplification? What's your goal?
Nov
30
comment Continuity of addition under the lower limit topology
i've corrected it...
Nov
27
comment compute exponential of matrix with wolfram alpha
Now I got it... MatrixExp is the right function to use.