17,321 reputation
43365
bio website mai.liu.se/~halun
location Linköping, Sweden
age 44
visits member for 4 years, 2 months
seen 5 mins ago

I liked this site better in the good old days when the questions were fewer and more interesting... I still drop in from time to time, though.


1m
comment When a function is non differentiable in every point does it mean that it has no instantaneous rate at every point?
If by "rate" you mean "derivative", then obviously if the derivative doesn't exist, the rate doesn't exist either...
12h
comment Differences between directional derivatives
Similar questions have been asked several times before here. Search for "mixed partial derivatives".
13h
answered How did Fourier series lead to the development of rigorous analysis?
22h
answered Error with mixed derivatives during derivation of Laplacian in polar coordinates
1d
comment Could negative integer factorials be defined in some way?
Analyticity is not enough to pin down $\Gamma$ uniquely; see Lucian's answer.
1d
answered $\int_y^x \cos(e^t)\,dt=(\sin(e^t))]_y^x$
1d
reviewed Approve suggested edit on Concerning crossproduct and orthonormality of vectors
1d
answered What is the change of basis in 2D?
1d
comment What is the change of basis in 2D?
I see, you mean matrix = "2-dimensional array" as in programming. In mathematics, "2D" usually refers to vectors with 2 coordinates, and 2-by-2 matrices...
1d
reviewed Approve suggested edit on L'Hospital's Rule to find limit
1d
comment Real analytic methods for the following integral
Just in case anybody is looking for that question: math.stackexchange.com/questions/958624/…
1d
comment How to calculate this kind of integral?
mathworld.wolfram.com/EllipticIntegral.html
1d
comment What is the formula to generate this number sequence : 1 , 7 , 14, 30
There's too little information here to give a meaningful answer.
2d
comment What is the change of basis in 2D?
This is a very strange question, unless you mean something else by "1D" and "2D" than the rest of the world... Could you try to clarify, please?
2d
comment What's the procedure for solving recurrence relations without coefficients?
That's definitely a linear ODE! If $y_1$ and $y_2$ are solutions, then so is $c_1 y_1 + c_2 y_2$ for any constants $c_1$ and $c_2$. But it has non-constant coefficients.
2d
comment Applying the Implicit Function Theorem from R3 to R
@user121270: You forgot a minus sign.
2d
comment What's the procedure for solving recurrence relations without coefficients?
@krey: It is linear. But the coefficients are not constant.
2d
comment Dividing by 2 numbers at once, what is the answer?
Mathematica uses $a/b/c=a/(bc)$, for example.
2d
comment How to compute $ \int e^{-st} \sin(2t) dt $
possible duplicate of Name of this identity? $\int e^{\alpha x}\cos(\beta x) \space dx = \frac{e^{\alpha x} (\alpha \cos(\beta x)+\beta \sin(\beta x))}{\alpha^2+\beta^2}$
Oct
20
comment A proviso in l'Hospitals rule
For the case $x \to \infty$ see this paper by Boas: maa.org/programs/faculty-and-departments/…