# mean hitting time

## Primary tabs

Defines:
mean hitting time
Type of Math Object:
Theorem
Major Section:
Reference

## Mathematics Subject Classification

60J10 no label found

## Comments

### Summation Sign

How do I get the j \in I to appear under the summation sign rather than to the right? I can't seem to get it to move.
Cheers

### Re: Summation Sign

$$\sum_{j \in I}$$ will do the trick.

But I'm not sure if $\sum_{j \in I}$ will work.
What is the difference, if someone knows?

### Re: Summation Sign

the difference is that  is better and  is evil (due to spacing handling).

Go br.endernet.org/~drini/TeX and get Sins of LaTeX2e to see what I'm talking about. I think there's a copy somewhere on CTAN too

Now to grandparent post: if you want the j\in I to show up below while the summation sign being inside a paragraph (instead of isolated centered equation) then please don't
(it will mess up interline space (might not be noticeable in HTML mode but it does in others) and make things look really ugly).

If you don't believe me, go for any calculus book and see how often to they use j\in I BELOW the summation and INSIDE a paragraph

f
G -----> H G
p \ /_ ----- ~ f(G)
\ / f ker f
G/ker f

### Re: Summation Sign

I'm trying to use it inside the array environment, to let me define a function in 2 cases, one of which includes a summation. I've made the entry public editable, so if someone can get it to work that would be great.

### Re: Summation Sign

I can fix it, but... which entry?
f
G -----> H G
p \ /_ ----- ~ f(G)
\ / f ker f
G/ker f

### PM.ORG Improvement WAS: Summation Sign

Oh it's mean hitting time

when one follows a post on htemain page
and such post comes from some encyclopedia article
there's no way to know which article it came from
since nor [up] link nor [top] will open the entry
f
G -----> H G
p \ /_ ----- ~ f(G)
\ / f ker f
G/ker f

### Re: PM.ORG Improvement WAS: Summation Sign

Thanks for doing that. The cases environment looks useful.

To get to the parent article from the main page, can't you just click the little planet by the post on the main page? Or when you're reading the message click the red up arrow? Both seem to work for me.

### Re: PM.ORG Improvement WAS: Summation Sign

ah ok, the little red arrow works when reading posts. It's just not so intuitive as the links BELOW the actual post
f
G -----> H G
p \ /_ ----- ~ f(G)
\ / f ker f
G/ker f

### Help with Formatting

Hi,
I'm trying to get a part of the proof to display right, but I just can't get it all aligned. I've commented it out, but would be grateful if someone could fix it for me and explain why it didn't work. (Its in mean hitting time if you're reading from the front page).
I've got a similar thing to do later in the proof, but I'll do that once I can see what I need to do differently.

Cheers

### Re: Help with Formatting

> Hi,
> I'm trying to get a part of the proof to display right, but
> I just can't get it all aligned. I've commented it out, but
> would be grateful if someone could fix it for me and explain
> why it didn't work. (Its in mean hitting time if you're
> reading from the front page).

What I can do is tell you what you seem to be doing wrong.

You must not put $...$'s inside an align' environment, its
contents are already in math mode. Also, put a \quad between
any math and following text. And put \usepackage{amsthm} in
your preamble so you can use the proof' environment
instead of \subsection{proof}. When you're not sure how to
make something look right, try checking the PM Content and Style
guide, it's liked to right above the editing box of the entry.

Finally, check your grammar. You have some slip ups with
subject-verb agreement in number.

Hope this helps.

### Re: Help with Formatting

Cheers. I had tried it without \$'s too, but I've now found my problem. I had accidentally typed \Sum instead of \sum. I've made the entry non world readable while i finish the proof.