69,027 reputation
145130
bio website math.ethz.ch/~blatter
location Switzerland
age 79
visits member for 4 years, 4 months
seen 7 hours ago

Nov
29
comment Is there a general notion of orientability, e.g. for the rationals?
@QiaochuYuan: I'd say that the rational projective plane is less orientable than ${\mathbb Q}^2$ is, and it should be possible to catch this fact using homogeneous coordinates.
Nov
29
comment Is this notation for inverse functions bad?
When you have reciprocals in the same discussion you could write $f^{-1}$ for the reciprocal and $f^{\leftarrow}$ for the inverse.
Nov
29
answered Elongation of edges of Moebius strip
Nov
28
comment Determining the list elements of $U = \{(A,B)\in \mathcal P(X) ×\mathcal P(X)\mid A=(X−B)\}$
This answer is wrong.
Nov
28
revised Roll 3 dice. Calculate the size of the event where the largest value of d1, d2, d3 is 6.
added 8 characters in body
Nov
27
revised function of three variable is even than $f(a,b,c)=f(|a|,|b|,|c|)$
deleted 33 characters in body
Nov
27
answered Roll 3 dice. Calculate the size of the event where the largest value of d1, d2, d3 is 6.
Nov
27
answered function of three variable is even than $f(a,b,c)=f(|a|,|b|,|c|)$
Nov
27
revised How to define the complex square root $ \sqrt{z} $?
deleted 28 characters in body
Nov
27
reviewed Approve German exercise - about “Normale im Wendepunkt”
Nov
27
comment $Ax=b$ what does solving it mean?
@MathIsHardNoItsNot: See my edit.
Nov
27
revised $Ax=b$ what does solving it mean?
added 159 characters in body
Nov
27
answered $Ax=b$ what does solving it mean?
Nov
27
comment Linear algebra and geometric insight: a rigorous approach to vector spaces, matrices, and linear applications
There are tons of textbooks doing exactly this, the mother of them all being Halmos' Finite dimensional vector spaces (1958).
Nov
27
answered How do you generally prove that the sum of a right triangle's hypotenuse and it's base have a common factor with the perpendicular side?
Nov
27
answered How many words can be written with $aabbbccdd$ such that no two equal letters are adjacent?
Nov
26
comment Find the indicial equation
Introducing a new independent variable $t$ such that $x=e^t$ transforms a given Euler differential equation into a differential equation with constant coefficients. It follows that the "algebraic theories" of these two types of differential equations are "isomorphic". The characteristic polynomial of constant coefficient equations appears as "indicial polynomial" in the case of Euler differential equations.
Nov
26
revised conformal mapping, regions of the complex plane marked +/-, find the function f,
added 86 characters in body
Nov
26
answered How to prove a function has no local minima.?
Nov
26
answered New proof about normal matrix is diagonalizable.