68,969 reputation
145130
bio website math.ethz.ch/~blatter
location Switzerland
age 79
visits member for 4 years, 4 months
seen 58 mins ago

15h
awarded  Constituent
16h
answered Directional derivatives exercise from Courant's introduction to calculus and analysis
18h
answered How to denote the set of all students who take the same class as some given student $s'$?
19h
comment To control first derivative with the function itself: $f'(x)^2\leq Cf(x)$ near where $f(x_0)=f'(x_0)=f''(x_0)=0$.
I'd suggest to precise the assumptions about $f$. It seems that $f$ is defined on all of ${\mathbb R}$ and $\equiv0$ outside some compact set. It is then impossible that $f'^2(x)<C f(x)$ for all $x\in{\mathbb R}$. What is meant by a "positive function" with compact support?
1d
answered Does there exist a 4D torus with a spherical cross-section, analogous to a circle for the 3D case?
1d
answered Solving trigonometric equation with unknown and restricted domain
2d
answered Question on notation: Using Conditional Sums to express the total distance traveled by a moving body with position $x=x(t)$
2d
comment Finding a limit using change of variable- how come it works?
This answer does not address the problem at all. It just regurgitates the state of limbo in which the OP sees himself.
2d
answered Does $\int_0^\infty |f'(x)| dx < \infty$ conclude $\lim_{x\to \infty} f(x)<\infty $
Dec
16
revised Proving that $\left( \frac{\partial^2}{\partial x^2} + \frac{\partial^2}{\partial y^2} \right) \lvert f(z) \rvert^2 = 4 \lvert f'(z) \rvert^2$
added 13 characters in body
Dec
16
answered How do you take the inner product of a vector whose components have different units?
Dec
16
answered Proving that $\left( \frac{\partial^2}{\partial x^2} + \frac{\partial^2}{\partial y^2} \right) \lvert f(z) \rvert^2 = 4 \lvert f'(z) \rvert^2$
Dec
16
answered How to exhibit the set of all the limit points of this subset of $\mathbb{R}^k$?
Dec
16
answered Counting candies in boxes
Dec
15
answered How many ways can the vertices of an equilateral triangle be colored using three different colors?
Dec
15
comment Solving $\sinh(ax) = bx$
What is the envisaged range of ${b\over a}\>$?
Dec
15
revised Do the properties of cauchy sequences carry over to converging functions?
added 4 characters in body
Dec
14
answered If $|z-3i|+|z-4|=5$ then find the minimum value of $|z|$
Dec
14
answered Do the properties of cauchy sequences carry over to converging functions?
Dec
13
answered Why does the determinate definition of the cross product give a vector that is perpendicular to the plane?