bio  website  math.harvard.edu/~elkies 

location  Harvard University, Cambridge, MA 02138  
age  47  
visits  member for  3 years, 2 months 
seen  4 hours ago  
stats  profile views  19,689 
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1d

awarded  Good Answer 
Jul 22 
revised 
Is this divisor ample on the product of two curves
added 187 characters in body 
Jul 22 
comment 
Is this divisor ample on the product of two curves
Thanks. I see that this was in fact a "Community" action. This question's score was zero, not positive, but the page you linked to says "nonnegatively scored" so a score of zero still fits that criterion. 
Jul 22 
comment 
True or false: if a set of 2D points has valid symmetry axes, then at least one of them is equal to a principal component vector
In practice this will usually work, but if the covariance matrix is scalar (or numerically indistinguishable from scalar) then every line through the origin is still a candidate symmetry axis. 
Jul 22 
answered  Is this divisor ample on the product of two curves 
Jul 21 
awarded  Custodian 
Jul 21 
reviewed  Leave Open How $f$ is approximated, in the $L^{p}$ norm, by a function $f+h$ whose Fourier transform is constant in some nbhd of the point? 
Jul 21 
reviewed  Leave Open Complex Phase Problem Relating to Binary Quadratic Forms 
Jul 21 
reviewed  Reviewed BMO spaces on the torus 
Jul 18 
comment 
Magic squares with specific properties
For $n=3$ there's a 5dimensional (affine) space of solutions, and it seems that generically there's no other subset that sums to $1$, so as long as you avoid a finite number of hyperplanes you're fine. 
Jul 15 
comment 
minimal conductors among elliptic curves with a fixed CM type
A bit more precisely, an elliptic curve has CM not by $K$ but by some order in $K$, i.e. a finiteindex subring of $O_K$. Usually that order must be $O_K$ itself, but there is one more choice for $d=4$ and $d=7$, and two more for $d=3$. In all but one of these four extra cases, specifying the CM ring does not affect the answer, because there's always a minimalconductor curve with endomorphisms by $O_K$ that's isogenous to $E$ (and isogenies preserve the conductor). But for $d=3$ there's an index2 subring ${\bf Z}[\sqrt{3}]$ of $O_K$ whose minimal conductor is not $27$ but $36$. 
Jul 13 
revised 
Incomplete Kloosterman sum
added 601 characters in body 
Jul 12 
comment 
Incomplete Kloosterman sum
…and there's a stray ")" in each instance of the denominator $e(b)1$. 
Jul 12 
awarded  Nice Answer 
Jul 12 
answered  Incomplete Kloosterman sum 
Jul 10 
answered  A calculation involving Lerch Transcendents 
Jul 8 
answered  Union of conjugates of a closed subgroup of a compact group 
Jul 7 
comment 
Points with minimal height
That looks as hard as deciding the existence of a rational point on an arbitrary variety $V/K$. Having found one $\phi(\beta)$ of low height, you can effectively find all points of lower height, but the preimage of each one is some variety $V/K$, and finding a rational point on $V$ is a system of Diophantine equations that can be as intractable as you wish. (It must be possible to rig things so that there's only one plausible candidate of height lower than $\phi(\beta)$ and this candidate yields your favorite $V$.) 
Jul 7 
comment 
Finding the set of all $01$ vectors in an affine subspace
For a finite projective plane (whether classical or not) there can't be any solution, because you're asking for a set $S$ of points that meets every line in just one point, but then $S>1$ and the line through any two points of $S$ yields a contradiction. 
Jul 7 
answered  intersection of the unit cube and a hyperplane containing the main diagonal 