Wolfram Mathematica

Q: Should we change the "bugs" tag name to something like "confirmed-bugs"?

3:53 AM

I want to answer this question:

Q: Random walk on a sphere

I'm trying to program a random walk on a sphere with Mathematica. I found this code while I was searching, but I'm not getting results from it. I waited an entire day, but my PC didn't finish evaluating rw. I would like some help please (: rotateWithAxis[p_, a_, theta_] := #/Norm[#] & @ ((1 –...

random

but I don't want to use my unilateral vote. Is anybody interested in reopening it?

Michael E2

@J.M. Yeah, not really sure why it was closed, given the upvotes to both Q and A.

1 hour later…

Karsten 7.

5:03 AM

@Wjx

I'm getting little bit tired of finding the Please don't use the BUGS tag until the community find confirmation there is a bug comment under most bugs questions.

discussion tag-synonyms

You should not introduce another bugs tag without a prior discussion on meta about it.

5:47 AM

Thanks for the reopen votes, guys!

Wjx

6:06 AM

alright, I think it may be helpful but it does not exist so I created one. sorry~

So, I think it would be helpful, why not create one?

6:44 AM

@Wjx then do write a proposal on meta so we can discuss it; on the other hand, have you seen the discussion Karsten linked to?

Wjx

7:12 AM

YEP~I think that will be good enough~

Maybe I will write a proposal~

2 hours later…

Szabolcs

9:04 AM

@Searke I'm just going to point out this in case it is of any help. I won't report it, I already report too much, so I'll stick to strictly bugs. I think this is interesting because if I am right in my assumption that Nothing aims to be an easier to use, less confusing version of Sequence[] then it seems to fail its purpose here.

But then one might argue that Query itself it already so complicated to use that discussions about keeping details simple are moot here.

I do find Query and Dataset quite hard to use ... :-( I think I need to spend more time with them.

Otherwise Nothing does look like a good idea. I think Sequence[] can't be used effectively without understanding Hold and Unevaluated well. I remember that when I first started using Mathematica, for a long time I was quite confused about these.

There's the Villegas tutorial, which explains them well.

Now we also have HoldForm, Defer, Delayed, Interpretation, Inactive, which are certain to confuse people ... especially Defer, which is really a Front End/Notebook feature, yet people keep trying to use it for evaluation control.

2 hours later…

A: Where does a package have to be loaded?

10:50 AM

I would like this answer to be as clear and compact as possible, feedback appreciated

tl;dr You need to call Needs before GetBoundaryMesh definition so it can be parsed correctly or you have to use the full name of ToBoundaryMesh. Confession My recent comment is partially incorrect $Context or $ContextPath changes (done by Get/Needs/BeginPackage and friends) are reflected a...

If you feel something is not clear or written in weird order, hit me.

1 hour later…

12:06 PM

@J.M.

Help please

Why cannot remove this three ```?

In this post

Could you help me improve that format?And tell me that reason?

@yode edited, is that what you need?

@Kuba

Yes,Thanks a lot

can you tell me the reason?

I have change it many times

@yode I'm not sure what was the problem, you mean that code was not formatted wiethout them?

Yes

@Kuba But you made it

12:22 PM

@yode when numbered or not list is started you have to indent code twice, notice 2x4 spaces there. And then the code block is aligned with a numbered item. How to make it aligned with base margin? I don't know other way than to put -------- separator before

Probably there is an easier way to break list but I wasn't motivated to search

@Kuba

But I don't know how to indent code twice

when I click the code button again,the sapce will disappear

@yode Indent once and the second time manually :) I hope there isn't anything like one click solution because it means I've lost a lot of time.

@Kuba Thanks :)

2 hours later…

2:28 PM

@Szabolcs Huh. I haven't really tried to use Nothing in a Query. From what I've seen, I like it.

Using Nothing with Query is one of those situations where I know nothing and don't understand the behavior, but also I would never even consider it and it's not probably a good idea.

It's like ordering Downvalues. I don't know @#$% about how Downvalues are ordered. I just write functions correctly to begin with so there's no tricky stuff doing on with the ordering of them.

Similarly, I have no $%^& idea what Nothing should do in a Query. I would never use it there because whatever it would be confusing and good code just wouldn't do that.

2:44 PM

@Searke "I just write functions correctly to begin with" - ideally everybody does that; practically... people have written stranger stuff.

I partially blame my software engineering education.

I had friends in engineering who had homework where there was some C code

and it was really ambiguous how it would execute.

and I'd tell them, you should add some parenthesis here so it's not ambiguous...

and they'd respond: "but that's not the homework problem. You're supposed to figure out what it would do?"

I can't understand the mindset of people who create such terribly unfun logic puzzles

@Searke It's not just programming; there are an awful lot of people who write as if parentheses were levied heavily.

I have a stack of books by Raymond Smullyan still to get thru before I handle those.

@J.M. and comments.

at the expense of people trying to read their stuff later, who then have the burning desire to scalp those writers for being too clever by half.

I'm more interested in understanding why the poster thought that Nothing would be a good thing to put into Query. I think that might be the actual problem worth solving.

2:50 PM

@Searke oh yes. Ideally (there's that word again!) one writes code that is plain as day, but most code definitely needs relevant and informative comments.

@Searke agreed.

Michael Hale

I've used Nothing on Datasets before. Like if I'm doing a Map and a Select, and the Map transformation uses an If or Switch, then I can skip the Select by transforming some of the values to Nothing.

Fair enough. But using Nothing as a function?

If you gave me Query[Nothing] and the documentation I probably wouldn't be able to tell you what it did.

Michael Hale

Can't say I've done that. The docs just say Nothing applied to anything just gives Nothing.

But who knows if Query Evaluates the Nothing before applying it? Who knows?

It's a fun logic puzzle. Maybe the real error is that Query doesn't scold you with a warning message that Nothing isn't valid input.

Michael Hale

My guess is that because Nothing isn't recognized as a part or filtering operation, then it is applied toward the end of the query as an ascending operator.

Szabolcs

3:17 PM

OK, maybe I didn't think very clearly about it.

BetweennessCentrality@GridGraph[{45, 45}] used to give a bad result, likely due to overflow. (This is a pathological graph for betweenness calculations.) In 10.3 it gives a good result. Great!!