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Topic: How to show 1+2+3+ ... = -1/12 using Mathematica's symbols?
Replies: 6   Last Post: Jan 23, 2014 3:25 AM

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 Andrzej Kozlowski Posts: 226 Registered: 1/29/05
Re: How to show 1+2+3+ ... = -1/12 using Mathematica's symbols?
Posted: Jan 22, 2014 3:27 AM

I think Knopp's book only discusses summation of convergent series (in the ordinary sense). The only book I know that gives a full and rigorous treatment of various methods of summation of divergent series is the book by Hardy Divergent Series that I have already mentioned. Like all of Hardy's books it is very elegantly and readably written (of course as long as you are one of those people who think that a whole page filled only with mathematical formulas can be called Creadable ;-) ).
In fact I only have a Russian translation of this book from 1951 (the original was published in 1949) and the translator states that no other comprehensive text on this topic exists. I think this is still the case more than half a century later.

The most classic book in English on the Cconventional theory of infinite series is probably Bromwich An Introduction to the Theory of Infinite Series, an electronic version of which can be downloaded freely and legally from the Internet. Obviously it does not discuss Ramanujan's ummantion. In fact, this is the text mentioned in the often quoted letter from Ramanujan to Hardy:

"Dear Sir, I am very much gratified on perusing your letter of the 8th February 1913. I was expecting a reply from you similar to the one which a Mathematics Professor at London wrote asking me to study carefully Bromwich's Infinite Series and not fall into the pitfalls of divergent series. ... I told him that the sum of an infinite number of terms of the series: 1 + 2 + 3 + 4 + ,,, -1/12 under my theory. If I
tell you this you will at once point out to me the lunatic asylum as my goal.

;-)

Andrzej

On 21 Jan 2014, at 23:57, Murray Eisenberg <murray@math.umass.edu> wrote:

>
> Do I correctly recall that Ramanujan summation is _not_ discussed in Knopp's classic book on infinite series?
>
> (I think I may have last closely studied it the German war-time recycled-paper edition Theorie ind Anwendung der unendlichen Reihen in 1960, for a seminar with Abram Besicovitch and I.J. Schoenberg.)
>
> Murray
>
> On Jan 21, 2014, at 3:24 PM, Andrzej Kozlowski <akozlowski@gmail.com> wrote:
>

>>
>>
>>
>> On 21 Jan 2014, at 19:58, Murray Eisenberg <murray@math.umass.edu> wrote:
>>

>>> Andrzej,
>>>
>>> Drat, I tried each documented value for the Regularization option except that one!

>>
>> Yes, the name CDirichlet for this summation (or =E2=80=9Cregularization=E2=80=9D) method seems to me non-standard but it =

was the only one that suggested a relation with the zeta function.
>> Hardy in =E2=80=9CDivergent Series=E2=80=9D called this summation =
method =E2=80=9CRamanujan summation=E2=80=9D, since Ramanujan used it =
all the time and obtained lots of formulas with it, although the =
classic =E2=80=9Cequality=E2=80=9D in this subject of this thread goes =
back to Euler.
>>
>> Andrzej
>>
>>

>>>
>>> On Jan 21, 2014, at 3:02 AM, Andrzej Kozlowski =

<akozlowski@gmail.com> wrote:
>>>
>>>> Note that:
>>>>
>>>> In[25]:= Sum[n, {n, 1, Infinity}, Regularization -> "Dirichlet"]
>>>>
>>>> Out[25]= -(1/12)
>>>>
>>>> This is of course, perfectly correct ;-)
>>>>
>>>> Andrzej
>>>>
>>>> On 20 Jan 2014, at 10:01, Murray Eisenberg <murray@math.umass.edu> =

wrote:
>>>>
>>>>> You may try the Regularization option for Sum, but it doesn't seem =
to give any finite result for that divergent series.
>>>>>
>>>>> On the other hand, the video to which you refer relies ultimately =

upon using Ces=E0ro-summability of 1 - 1 + 1 - 1 _ . . . , which you =
may implement in Mathematica as:
>>>>>
>>>>> Sum[(-1)^n, {n, 0, \[Infinity]}, Regularization -> =93Cesaro"]
>>>>> (* 1/2 *)
>>>>>
>>>>> [The video to which you refer is disingenuous in not saying =

up-front that it's not using ordinary summability but some other form(s) =
of summability. (The merest hint is a brief glimpse of a page of a text =
on String Theory where the formula
>>>>> 1 + 2 + 3 + . . . = -1/12 is displayed just below a line =
referring to renormalization.)
>>>>>
>>>>> As it stands, that video, in my mind, is deleterious to =

understanding of the mathematics of infinite series destructive of trust =
in mathematics: it manipulates divergent series as if they were =
convergent.]
>>>>>
>>>>>
>>>>> On Jan 19, 2014, at 2:56 AM, Matthias Bode <lvsaba@hotmail.com> =

wrote:
>>>>>
>>>>>>
>>>>>> Hola,
>>>>>>
>>>>>> I came across this video (supported by the Mathematical Sciences =

Research Institute* in Berkeley, California):
>>>>>>
>>>>>> http://www.numberphile.com/videos/analytical_continuation1.html
>>>>>>
>>>>>> Could the method shown in this video be replicated using =

Mathematica symbols such as Sum[] &c.?
>>>>>>
>>>>>> Best regards,
>>>>>>
>>>>>> MATTHIAS BODES 17.36398=B0, W 66.21816=B0,2'590 m. AMSL.
>>>>>>
>>>>>> *) http://www.msri.org/web/msri
>>>>>>

>>>>>
>>>>> Murray Eisenberg =

murray@math.umass.edu
>>>>> Mathematics & Statistics Dept.
>>>>> Lederle Graduate Research Tower phone 240 246-7240 (H)
>>>>> University of Massachusetts
>>>>> 710 North Pleasant Street
>>>>> Amherst, MA 01003-9305
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>

>>>>
>>>>

>>>
>>> =E2=80=94=E2=80=94
>>> Murray Eisenberg =

murray@math.umass.edu
>>> Mathematics & Statistics Dept.
>>> Lederle Graduate Research Tower phone 240 246-7240 (H)
>>> University of Massachusetts
>>> 710 North Pleasant Street
>>> Amherst, MA 01003-9305
>>>
>>>
>>>
>>>
>>>
>>>

>>
>
> =E2=80=94=E2=80=94
> Murray Eisenberg murray@math.umass.edu
> Mathematics & Statistics Dept.
> Lederle Graduate Research Tower phone 240 246-7240 (H)
> University of Massachusetts
> 710 North Pleasant Street
> Amherst, MA 01003-9305
>
>
>
>
>
>

Date Subject Author
1/22/14 Andrzej Kozlowski
1/23/14 Murray Eisenberg
1/23/14 Andrzej Kozlowski