The idea is to replace $\sum_{i=0}^\infty$ in $$\sum_{i=0}^\infty a_n = a$$ with some other operator $T$ that replicates some features of $\sum$. The simplest example is the alternating ones. Instead of summing, you can take the average of the partial sums
for a_n = 1,-1,1,-1,1,... standard partial sums s_n = 1,0,1,0,1,0,... and the average of partial sums is 1, 1/2, 2/3, 1/2, 3/5, ... which does converge to 1/2 if you check it right
if a series converges normally, then it "converges" in this sense as well, and to the same "sum". And its linear, like summation. So it somehow manages to extend summation of usual convergent series
this is called Cesaro summation, but not everything about summation is preserved. If you put in lots of zeros, i.e. replace a_1+a_2+a_3+... with a_1+0+..+0+a_2+0+... then you can spoil Cesaro summability
Tao observed that this and other generalised summability methods work by "smoothing" the sharp cut-off in the partial sum
I'll leave it at that for now and drop some resources. First, there should be many places for Cesaro summation, since it is known that Fourier series of continuous functions Cesaro-converge back to the original function. I would guess a readable intro to Fourier analysis is Stein and Shakarchi's first book.
A book specifically devoted to divergent series is Hardy's Divergent Series
The fact that the Fourier series of continuous functions Cesaro converges is not because it converges normally. See third-last paragraph of 'Pointwise Convergence' section in this wiki page: en.wikipedia.org/wiki/…
Fourier series in general could be another idea. Cantor originally started studying trigonometric series and decided that in order to answer the questions he had to first improve what we understand about sets jstor.org/stable/41133951
In mathematics, the moving sofa problem or sofa problem is a two-dimensional idealisation of real-life furniture-moving problems and asks for the rigid two-dimensional shape of largest area A that can be maneuvered through an L-shaped planar region with legs of unit width. The area A thus obtained is referred to as the sofa constant. The exact value of the sofa constant is an open problem.
== History ==
The first formal publication was by the Austrian-Canadian mathematician Leo Moser in 1966, although there had been many informal mentions before that date.
== Bounds ==
Work has been don...
To me, axiom of choice seems a bit too boring of a topic compared to other topics on the big list =P Logicians and Set-theorist and Philosophers are interested in these kinds of things.
In mathematics, a Padé approximant is the "best" approximation of a function by a rational function of given order. Under this technique, the approximant's power series agrees with the power series of the function it is approximating. The technique was developed around 1890 by Henri Padé, but goes back to Georg Frobenius, who introduced the idea and investigated the features of rational approximations of power series.
The Padé approximant often gives better approximation of the function than truncating its Taylor series, and it may still work where the Taylor series does not converge. For these...