 11:11 PM
0  I noticed for the first time today that there is a (block-design) tag, with no description and 12 questions. It seems that this tag is completely redundant, as there is already a (combinatorial-designs) tag (which does have a description, 154 questions, and is the exact same thing). Should this t... 11:36 PM
The tag has been created in July.
Jul 3 '17 at 14:20, by Martin Sleziak
Some new tags: and .
The tag is already at 58 questions.
The new tag seems basically as a meta tag to me.
3  If $a_k = c^k-1$, where $c > 1$, what can be said about $s(n) =\sum_{k=1}^n \dfrac{a_k}{a_{k+1}}$? This is a generalization of $a_n=3^n-1$, prove that $\frac{a_1}{a_2}+\frac{a_2}{a_3}+\dots+\frac{a_n}{a_{n+1}}>\frac{n}{3}-\frac{1}{8}.$ which is the case $c=3$. I can show that $\dfrac{n}{c}-\df... I have removed it from the post. We will see what happens next - if it's created again I can make a post on meta. It seems that the same tags has been created in the past: data.stackexchange.com/math/query/787716/… - there was one occurrence in 2012 and one in 2016. The same query did not find anything with the British spelling: data.stackexchange.com/math/query/787716/… Another new tag was created by Rodrigo de Azevedo. He also created the tag-excerpt: "CVXPY is a Python-embedded modeling language for convex optimization problems." 0  I am trying to use CVXPY on a mixed-integer program. One of my constraints is of the form $$y = \begin{cases} g(x) & f(x)\geqslant m\\ 0 & \text{otherwise} \end{cases}$$ for affine functions$f$and$g$. My construction is$y=\mathbb{I}_{\{f(x)\geqslant m\}}\cdot g(x)\$, where I can linearize t...

A bit more about on meta:
I asked in a comment, when the tag appeared, whether it was sufficiently different from combinatorial-designs. The tag creator seemed to feel it was. I'll add a comment to that thread, pointing to this Meta one. — pjs36 3 mins ago
It looks like this question created the tag block-design. Just an FYI, there is also the tag [combinatorial-designs]; do you think these two are sufficiently different to warrant both? Or should one subsume the other/should a synonym be created? (I'm interested in designs but I don't know much; just an honest question) — pjs36 Jul 14 '17 at 10:50
@pjs36 I'd have to look into combinatorial designs to be certain, but that sounds a fairly general term. Block design is a highly precise term; see the Wikipedia article. I made the new tag deliberately, if that counts for anything, after being startled it didn't exist. — Wildcard Jul 14 '17 at 10:54
A Meta discussion has just started around the tag block-design, you might be interested in weighing in. — pjs36 2 mins ago Block design
In combinatorial mathematics, a block design is a set together with a family of subsets (repeated subsets are allowed at times) whose members are chosen to satisfy some set of properties that are deemed useful for a particular application. These applications come from many areas, including experimental design, finite geometry, software testing, cryptography, and algebraic geometry. Many variations have been examined, but the most intensely studied are the balanced incomplete block designs (BIBDs or 2-designs) which historically were related to statistical issues in the design of experiments. A... Combinatorial design
Combinatorial design theory is the part of combinatorial mathematics that deals with the existence, construction and properties of systems of finite sets whose arrangements satisfy generalized concepts of balance and/or symmetry. These concepts are not made precise so that a wide range of objects can be thought of as being under the same umbrella. At times this might involve the numerical sizes of set intersections as in block designs, while at other times it could involve the spatial arrangement of entries in an array as in sudoku grids. Combinatorial design theory can be applied to the area of...