My Math Forum Finite mapped on infinite set

 Number Theory Number Theory Math Forum

February 27th, 2018, 02:12 PM   #11
Senior Member

Joined: Aug 2012

Posts: 2,411
Thanks: 754

Quote:
 Originally Posted by Loren topsquark seems to have defined most closely to what I was getting at -- say p(-1) representing all negative integers, perhaps a surjective function. I think my main concern is whether one may repeat beyond limit identical elements of the domain (below). Would "exactly" allow that?
Are you thinking perhaps of something like a Riemann surface?

In complex variable theory, the square root function $w = \sqrt{z}$ has two distinct outputs. Unlike in the case of a real variable, there's no algebraic way to distinguish them (for example by choosing the positive one by convention. There are no positive or negative complex numbers).

There are two ways to address this problem. One is by "choosing a branch." When you specific a multi-valued complex function, you also need to say which output value you're choosing. You can always do this in a consistent manner. [I'm leaving out a lot of technicalities with that statement].

The other way is to consider all the outputs at once, as a single geometric structure. The Wiki article contains some nice pictures of how this works.

 February 27th, 2018, 09:21 PM #12 Senior Member   Joined: May 2015 From: Arlington, VA Posts: 464 Thanks: 29 Math Focus: Number theory I recall that z^(1/2) could be represented on the unit complex circle by half its perimeter between z and real value one. Of course, the circle has countless rotations corresponding to the arc from z^(1/2) to the above mentioned complex origin, thus one complex number would project to innumerable others. Would this establish a mapping from a finite set (that of the complex number z) to a set of limitless corresponding rotations? Or is a circle disqualified for not being a function, although the results are unique? Did Riemann consider this approach, if tenable? In principle, can there exist a finite set of functions which map onto a set of unique, countless solutions?

 Tags finite, infinite, mapped, set

 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post IAmABread Abstract Algebra 13 June 8th, 2017 12:27 PM Luiz Real Analysis 5 April 22nd, 2015 10:15 AM Luiz Real Analysis 4 April 8th, 2015 05:56 AM Luiz Real Analysis 1 April 4th, 2015 11:58 AM mathdigger Number Theory 5 September 3rd, 2010 09:37 PM

 Contact - Home - Forums - Cryptocurrency Forum - Top