Where the complex points are (2016)

Where the complex points are (2016)

Whilst you first research superior numbers, you gape out that they provide the system to unravel equations that had been beforehand unsolvable. The usual occasion is the equation equation x^2 + 1 = 0, which while you occur to’re totally the make the most of of actual numbers has no alternate concepts, however with superior numbers has the alternate concepts x=i and x=-i.

As any individual who likes to agree with the bodily actuality of all of the items, this has on a regular basis launched on me considerable difficulties. The equation x^2 + 1 = Zero could possibly be considered the equation that tells you the hold the parabola with equation y = x^2 + 1 meets the x-axis.

Handiest the parabola with equation y = x^2 +1 doesn’t meet the x-axis. If our superior quantity alternate concepts are to be believed, then it meets the x-axis within the capabilities (i,0) and (-i,0), however I utterly can’t glimpse these capabilities on my graph. The place are they?


Presumably there are a complete host of capabilities with superior coordinates, which could possibly be capabilities the hold diverse issues meet that don’t gaze like they meet. These capabilities desires to be someplace, and in order that they desires to be some self-discipline that’s by some capacity associated to the graphs I glimpse within the true plane. Nonetheless the hold is that this self-discipline?

Correctly, about per week beforehand, I at closing came upon the self-discipline the hold the superior capabilities are!

(At this level I have to obtain a few issues certain: I really grasp made this up completely on my very personal. I really grasp not found it from any individual else, or from discovering out any individual else’s work. I am not so useless as to mediate that no-one has ever even handed this prior to, however as but I can’t salvage search phrases in Google which grasp proven me the leisure shut. Whilst you grasp heard of it prior to I’d like to know!)

Proper right here’s the muse: at each level within the true plane, there are an accurate-aircraft’s-price of superior capabilities connected. The superior capabilities connected to the true level (a,b) are the entire set up (a+ci,b+di). That’s, the true substances of the 2 coordinates are (a,b). I agree with them as a plane, with x-axis exhibiting what imaginary phase we’ve added to the x-coordinate, and y-axis exhibiting what imaginary phase we’ve added to the y-coordinate.The true level itself is within the centre of this plane.


I’m going to name this plane connected to the purpose (a,b) the “iplane at (a,b)”. Within the picture above, I’ve proven a few capabilities within the iplane at (3,2). I’ve coloured it pink in order that it is good to nicely additionally articulate it’s not the long-established actual plane, which as you noticed above, I usually colour in white.

After I order “connected” I imply it actually — I really obtain agree with the iplane being connected to the purpose in a bodily sense, like within the images right here, which could possibly be at diverse ranges of unfold-out-ness:


With out a doubt, each level within the true plane has its personal iplane, so the superior plane as a complete seems extra like this:


And that’s the hold the superior capabilities are. The superior level (3+i,5-2i) is within the iplane connected to the true level (3,5); the superior level (2i, -6+7i) is within the iplane connected to the true level (0,-6); and the superior capabilities (i,0) and (-i,0) are each within the iplane connected to the true level (0,0).

It’s extra easy to glimpse them while you occur to unfold the last word iplane out and flatten it so it sits on high of the true plane. You don’t are searching for to obtain the entire plane really; you merely want a large ample prick in order that you can also glimpse the hold the purpose is that you really want. Additionally, I agree with the iplane being clear in order that it is good to nicely additionally glimpse the true plane through it — therefore the cellophane to your complete images of the bodily fashions.

Within the beneath characterize, a prick of the iplane at (0,0) is being flattened out to show conceal the capabilities (i,0) and (-i,0).


This GeoGebra applet lets you enter the coordinates of a fancy level and this will even show conceal you the iplane it’s in and the true level the hold the iplane is connected. Give it a rush to obtain a really feel for what’s occurring right here.


So why am i so very very indignant by this conception? Correctly, all of it has to obtain with what happens while you occur to find out the superior capabilities which could possibly be phase of some acquainted graphs. Beforehand, I’ve thought rather a lot about traces and considerably about parabolas. This is ready to presumably make a alternative me some time to jot down down about all of it, so I’ll set up these topic points for the next weblog posts.

As I write them, I’ll put hyperlinks right here to the alternative posts:


  1. Not a mathematician so correct away:

    I think the initial confusion stemmed from not pinning down the domain of x and y.

    When he says “I don’t see the complex points” in the xy graph that is because they aren’t there: the xy graph is in R^2 and x^2 + 1 = y has no solution in the reals for y = 0.

    But if you imagine, as he did, an extra dimension attached at each point then that is now a complex space, is it not?

  2. I think about it quite differently.

    A function in the complex plane is a 4-dimensional thing. A graph of that function on the real plane is a 2-D slice of that 4-D thing.

    That said, the one visualization of complex numbers that I wish more understood was a complex number in polar coordinates. In polar coordinates, addition is complicated. But multiplication is simple. Every complex number is a magnitude and an angle. You multiply the magnitudes and add the angles.

    What this means is that -1 is (1, 180 degrees). Literally a turn halfway around the circle. And now what are its square roots? Well i is (1, 90 degrees) and -i is (1, -90 degrees). Now stand up and actually do those turns.

    The result is that i is a turning motion that takes you off the real line. But that visualization helps build intuition about why in the complex plane there should be a close connection between exponential functions and sin/cos. (Specifically e^(ix) = cos(x) + i sin(x) – in other words it is a turn by x radians.)

  3. It's always appreciable to try to comprehend stuff through new ways and tools, but I fail to see the aim of the post. Isn't it a matter of properly defining the domain of application and associating a way to visualize it?

    Representing the result of a function from R to R requires two orthogonal axes because the element pre-transformation is 1-dimensional and the result is also 1-dimensional.

    For C to R, this would require 2+1=3 orthogonal axes, so it can be visualized with a 3D representation. Likewise for R to C.

    From C to C that would be 4-dimensional and becomes already trickier without some effort to conceptualize it, and certainly becomes less intuitive without resorting to alternate ways to conceptualize dimensions.

    It quite probable that beyond that, one would really encounter decreasing returns on trying to visualize the situation because the cost of abstraction would increase in order to rely on multisensorial approaches to compensate for our inability to visually perceive much beyond 3D.

    It's entirely possible that the whole post flew way over my head and I absolutely did not get it though, in which case I am truly just a confused commenter.

  4. I find this less intuitive than simply looking at the real component, imaginary component, magnitude, and phase plots of simple, and then progressively more complicated functions of interest.

    For example, starting with y = x^2+1:


    You can see that the real component has a hyperbolic parabaloid shape. The imaginary component does too, just rotated by 45 degrees. This shape clearly has zeroes, since it's continuous and has infinite range. You can try to look for spots where both components are zero, or you can plot the magnitude:


    You can then clearly see that the zeros are "out" and below the global minimum of the real plot.

    You can only really look at a slice at a time, but I find this easier than the crumpled-paper-at-every-point approach, because it's a lot harder to see patterns emerge in nearby bits of crumpled paper.


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