Issue 10562: Change 'j' for imaginary unit into an 'i'

http://bugs.python.org/issue10562

by redacted • 16 years ago

48 54 16 years ago

bugs.python.org

joss822• 16 years ago

Who ever use imaginary/complex numbers anyway?

pohl• 16 years ago

http://en.wikipedia.org/wiki/Complex_number#Applications

CamperBob• 16 years ago

If you rotate your phone's keypad 90 degrees, you can call Hogwarts!

To actually answer your question, complex numbers make signal processing algorithms much more tractable, and also make it easy to visualize many commonplace quantities and phenomena in electrical engineering. Anytime a value has both a magnitude and a time- or phase-based aspect, chances are you can use complex numbers to represent it.

Put another way: just as negative numbers allow you to specify movement along an axis, complex numbers allow you to specify rotation around an axis. Both are obviously pretty fundamental.

tomjen3• 16 years ago

Wouldn't the same advantage be obtained by x and y coordinates?

joss822• 16 years ago

Sure, but have you ever used them in a real world project? And outside of academics?

timmorgan• 16 years ago

I think it was a valid (though poorly worded) question. Not really deserving -4. Thanks for the answers anyway -- I haven't touched imaginary numbers since high school.

alan-crowe• 16 years ago

They are important for factorising prime numbers. For example

17 = (4+i)(4-i)

camtarn• 16 years ago

j vs i gets really confusing when you're doing a dual electrical engineering / computer science degree, since you have to remember which classes use which: electrical engineering uses j (since i is already taken to mean current), CS math uses i :)

rikthevik• 16 years ago

I said something about j in my number theory class after 3 years of EE and my professor looked at me like I was an idiot. He apparently had never heard of j once in his life.

podperson• 16 years ago

It's surprising to me that a programming language would have started out following engineering conventions rather than mathematical conventions, even if there's a strong overlap between EE and CS. That said (and speaking as a mathematician) I think it's foolish to use j over i, especially since in some cases (e.g. quaternions) it will be very confusing.

brlewis• 16 years ago

Agreed. Scheme uses i and not j, and it was created at MIT, where there isn't even a separate CS department, just EECS.

hugh32• 16 years ago

Physicists, on the other hand, have come to terms with the fact that they have fewer letters in the English and Greek alphabets than concepts they need to express, and so happily overload i and everything else, hoping to always figure it out from context.

treo• 16 years ago

just add a hat ^ or squiggle ~ over it, or maybe a point, or something else. I always wondered when the Hebrew alphabet would come up.

kd5bjo• 16 years ago

Not really. Python only supports the second square root of -1 instead of the first at the moment. They are indistinguishable from each other until you introduce the other two. It's just convention that the first one is what's in common use when you don't need all three.

nas• 16 years ago

The decision to use "j" was made quite a long time ago by Guido. There as a fairly short discussion about it and he made his decision. As other people have said, this is a bike shed issue. BTW, Guido's MSc is in math.

adambyrtek• 16 years ago

What happened to "there should be one-- and preferably only one --obvious way to do it"?

PS. I've also posted this as a comment to the bug report.

random42• 16 years ago

This is python's philosophy. However the ambiguity is due to different representation in other known fields, namely engineering and mathematics.

PS - I agree, (and upvoted) to your comment. I like this approach http://bugs.python.org/issue10562#msg123135

cap10morgan• 16 years ago

That page could be added to the list of classic examples of bike-shedding.

gjm11• 16 years ago

Except that the bikesheddiest bits are deliberate satire.

jacobolus2• 16 years ago

I feel a bit bad for Retro, and half hold out the hope that he’s an invented character just playing a role.

briancurtin• 16 years ago

A lot of the issues he creates are very low priority or invalid , but he aggressively, un-cooperatively, and repeatedly pushes that they be fixed.

colinprince• 16 years ago

I love this:

I'm personally -0.small on it

even though I don't understand it. Anyone?

jacobolus2• 16 years ago

In the Python community, agreement with a proposed change (“this is a good idea”) is indicated by +1, disagreement (“this is a bad idea”) is indicated by -1, and mostly indifference leaning slightly for or against (as in “I (dis)approve but don’t really care”) is indicated by +0 or -0. My guess is that -0.small is intended to mean something like “I slightly disapprove but this is utterly insignificant”.

Edit: much more amusing is Antoine’s comment “[...] Otherwise +11j from me”

skorgu• 16 years ago

I'd parse it to be "opposed to it but only very slightly." Similar to -σ maybe.

baq• 16 years ago

probably a representation of a value smaller than 0 but larger than the nearest-to-0 possible value that can be encoded as a floating point number (that still isn't 0). or something like that.

bobds• 16 years ago

My favourite part:

"That could work; it's a bit late to do this in 3.2, though. How about the following transition strategy for the complex output.

Python 3.3: Introduce PYTHONIMAGINARYSYMBOL environment variable (and possibly also a related command-line option to the interpreter?).

Python 3.4: Show a warning on startup if this environment variable isn't used.

Python 3.5: Make the environment variable mandatory.

Python 3.6: Make the environment variable optional again, but this time with the default output being 'i' rather than 'j'.

Python 3.7: Deprecate use of PYTHONIMAGINARYSYMBOL. (Warning on startup if it's set.)

Python 3.8: Error on startup if PYTHONIMAGINARYSYMBOL is set.

Python 3.9: Go back to ignoring PYTHONIMAGINARYSYMBOL."

mgedmin• 16 years ago

Mine was

"This deterministic approach has the advantage that migration of code from one imaginary symbol to another is as easy as:

sed -e 's/k/l/' -e 's/j/k/' -e 's/i/j/' -e 's/l/i/'

provided that you restrict yourself not to use the characters i, j, k or l in identifiers, keywords or strings in the source code."

jcdreads• 16 years ago

I know that cooler heads will prevail, and that python won't get this silly syntax change, but...

...everyone seems to be forgetting that i == -j (either squared is 1). Physicists usually describe traveling waves (of whatever) as something proportional to exp(kx-iwt) where that's an omega, not a w, and electrical engineers for whatever reason prefer the notation exp(kx+jwt) (note the minus sign difference). Except ee's sometimes write exp(kx-jwt), depending on the convention in use at the time.

Jun8• 16 years ago

The reason is that i is used to denote (time changing) current in electrical engineering.

juiceandjuice3• 16 years ago

What are you talking about? i == j, and either squared are equal to negative one. You can use them interchangeably.

tome• 16 years ago

You can use i and -i interchangably, as long as you're consistent.

YuriNiyazov2• 16 years ago

Take a look at quaternions (http://en.wikipedia.org/wiki/Quaternion) where ii == jj == -1, but i != j

iwr2• 16 years ago

i(j) squared is -1 if we're talking about complex numbers and 1 for split-complex numbers. Each is an interesting class of numbers.

wnoise• 16 years ago

It's an imaginary number, not a jimaginary number.

ez772• 16 years ago

What module are they talking about? Could someone give an example? For instance, the following doesn't work:

  import math
  math.sqrt(-1)

vault_• 16 years ago

That would be the 'cmath' module.

ez772• 16 years ago

Thank you. Clearly a python noob here...

Issue 10562: Change 'j' for imaginary unit into an 'i'

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