Opened 7 years ago
Closed 7 years ago
#1576 closed enhancement (fixed)
[with patch; very positive review] implicit multiplication -- sage needs to have *some* way to do this (even if not by default)
Reported by: | was | Owned by: | robertwb |
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Priority: | major | Milestone: | sage-2.9.2 |
Component: | calculus | Keywords: | |
Cc: | Merged in: | ||
Authors: | Reviewers: | ||
Report Upstream: | Work issues: | ||
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description
Here are some examples that should probably work (from somebody named amscopub-travel)
As per an irc conversation last week, here is a list of math expressions using implicit multiplication. Sorry for the delay:
a b c(a^2 + b^2 + c^2) a b + c^2 == y (z/(2sin(y z/55))+y+x)^(z/(2sin(y z/55))+y+x) 2(x/2)^2+4(2x)^2 0==-16x^2+48x (x+2)(x-1) x^2-4x+4 2(x+3)(x-4) 2x^2-2x-25<=0 -16x^2+132x 2(x+3)(x-4) x^2-5x+4 3(x-5)(x-5) (x-1)(x-2)x (a-b)(a-b)(a-b) Take any usual python expression and drop the multiplication operator (or really make it *optional*). So for example, 2*x would be 2x. However, when ambiguity would result in variable names, use * or a space. For example, a*b*c would be a b c (to distinguish from the variable "abc").
A first version of this could simply be a function
implicit_mul
that takes a string as input, and outputs
Attachments (1)
Change History (7)
comment:1 Changed 7 years ago by robertwb
- Owner changed from was to robertwb
- Status changed from new to assigned
comment:2 Changed 7 years ago by robertwb
Changed 7 years ago by robertwb
comment:3 Changed 7 years ago by robertwb
- Summary changed from implicit multiplication -- sage needs to have *some* way to do this (even if not by default) to [with patch] implicit multiplication -- sage needs to have *some* way to do this (even if not by default)
comment:4 Changed 7 years ago by was
- Summary changed from [with patch] implicit multiplication -- sage needs to have *some* way to do this (even if not by default) to [with patch; very positive review] implicit multiplication -- sage needs to have *some* way to do this (even if not by default)
This is frickin awesome!
I think we should just enable this by default via the preparser.
WOW!
This is very nice to work with.
comment:5 Changed 7 years ago by was
william_stein: I just reviewed #1576 [09:02am] william_stein: It makes stuff like this work: [09:02am] william_stein: sage: 2x^2-2x-25<=0 [09:02am] william_stein: 2*x^2 - 2*x - 25 <= 0 [09:02am] william_stein: sage: sin(2x) [09:02am] william_stein: sin(2*x) [09:02am] william_stein: sage: var('a,b,c') [09:02am] william_stein: (a, b, c) [09:02am] william_stein: sage: a b c(a^2 + b^2 + c^2) [09:02am] william_stein: a*b*(c^2 + b^2 + a^2) [09:02am] william_stein: But doesn't break anything. [09:02am] william_stein: That last looks funny. [09:03am] william_stein: It's because we still have implicit calling... [09:06am] mabshoff: ok, is there any way you can give me some rights in the wiki to delete users? [09:06am] mabshoff: Certain spammers are either comming back again and again or a re [09:06am] mabshoff: registering under the same name over and over again. [09:06am] mabshoff: mhansen did suggest installing a text based captcha, which should stop all the [09:06am] mabshoff: machine driven spam. [09:06am] mabshoff: I see. I don't like that to be enabled by default. What happens for Q[x,xy,y] ? [09:06am] mabshoff: Then if you write xxyyx - what is that? [09:06am] mabshoff: Or does that get covered by the patch? [09:06am] mabshoff: the last one is *wrong*. Or what does c() do? [09:06am] mabshoff: If c is a var it should be 'a*b*c*(...)' [09:07am] william_stein: Just apply only the first patch posted and not the second. [09:07am] william_stein: Then nothing happens by default. [09:07am] william_stein: There are levels of implicit multiplication, by the way. [09:07am] william_stein: In the future when c(...) is an error, that example above would raise an error. [09:07am] mabshoff: Sure. We did discuss implicit multiplication a lot during the CoCoA language [09:07am] william_stein: The default is not to do anything with the c (...) implicit mulitplication. [09:07am] william_stein: But it works quite well in all other cases that I tried. [09:07am] mabshoff: design specification and we came to the conclusion that it is evil. [09:08am] william_stein: I like what Robert did. [09:08am] william_stein: Singular has implicit mult also. [09:08am] mabshoff: Does Maple or Mathematica let you do that? [09:08am] william_stein: Maple doesn't I think. Mathematica certainly does and the users love it. [09:08am] mabshoff: Sure, but it complicates the language parser enourmously. [09:08am] william_stein: not for sage [09:08am] mabshoff: What about newlines? Are they ignored, i.e. [09:08am] mabshoff: a [09:08am] william_stein: It was a half page of code. done. [09:08am] mabshoff: b [09:08am] mabshoff: it that a*b ? [09:08am] william_stein: Python is way simpler! [09:09am] william_stein: a and b are completely different statements [09:09am] mabshoff: I believe you. [09:09am] william_stein: and if you do "a backslash b" then it gets turned into one line before pre-parsing. [09:09am] mabshoff: Because if you allow implicit multiplication accross lines all hell breaks loose. [09:09am] mabshoff: Sure, in that case it is deliberate and the user implies that those are meant to be one line. [09:10am] william_stein: In Python "across lines" sort of disappears... [09:10am] mabshoff: I don't mind it being there, I just think that turning it on per default is bad. [09:10am] william_stein: I disagree. [09:10am] mabshoff: [09:10am] william_stein: But for 2.9.2 turning on by default is bad. [09:10am] william_stein: For 2.10 it may be different. mabshoff: Well, ther certainly will be bugs to shake out, so I agree totally with merging the first patch [09:10am] mabshoff: for 2.9.2. and then sort out the rest in 2.10 [09:10am] william_stein: good
comment:6 Changed 7 years ago by mabshoff
- Resolution set to fixed
- Status changed from assigned to closed
Merged in 2.9.2.rc1.
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I've implemented implicit_mul, the output for the above expressions are:
There is an optional flag, level, which at the highest value produces:
Which could be bad, for example f(x)(y) would become f(x)*(y). In the first case, I have no idea how to deduce that c shouldn't be called.
At all but this highest level, I believe it never mangles valid Python. Just to test, I pre-parsed the entire SAGE library through this function and there were no changes.
Some more examples:
This is not yet on by default.