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# Quick Questions, Short Answers - No Debate

Author Topic:   Quick Questions, Short Answers - No Debate
AZPaul3
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From: Phoenix
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 Message 586 of 650 (876229) 05-14-2020 10:05 PM

Latex Help
Trying to write Einstein equation.

Can't get mu, lambda or pi into equation - displays as invalid equation

G_{µv}+Λg_{µv}=\frac{8πG}{c^4}T_{µv}

Will not resolve.

$\color{white} G_{µv}+Λg_{µv}=\frac{8πG}{c^4}T_{µv}$

take out the mu, pi and lambda

G_{v}+g_{v}=\frac{8G}{c^4}T_{v}

-- Latex resolves just fine.

Try putting only one mu in

G_{µv}+g_{v}=\frac{8G}{c^4}T_{v}

$\color{white} G_{µv}+g_{v}=\frac{8G}{c^4}T_{v}$

Take out mu put in lambda

G_{v}+Λg_{v}=\frac{8G}{c^4}T_{v}

$\color{white} G_{v}+Λg_{v}=\frac{8G}{c^4}T_{v}$

Take out lambda put in pi (which copies in as greek uppercase P - Why?)

G_{v}+g_{v}=\frac{8πG}{c^4}T_{v}

$\color{white} G_{v}+g_{v}=\frac{8πG}{c^4}T_{v}$

What did I miss?

Factio Republicana delenda est.

 Replies to this message: Message 587 by nwr, posted 05-15-2020 12:49 AM AZPaul3 has responded

nwr
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From: Geneva, Illinois
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 (2)
 Message 587 of 650 (876232) 05-15-2020 12:49 AM Reply to: Message 586 by AZPaul305-14-2020 10:05 PM

Re: Latex Help
Is this what you are looking for?

Remember that latex is all ascii. It doesn't know about fancy character sets.

Fundamentalism - the anti-American, anti-Christian branch of American Christianity

 This message is a reply to: Message 586 by AZPaul3, posted 05-14-2020 10:05 PM AZPaul3 has responded

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AZPaul3
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Posts: 6007
From: Phoenix
Joined: 11-06-2006
Member Rating: 3.5

 Message 588 of 650 (876237) 05-15-2020 5:40 AM Reply to: Message 587 by nwr05-15-2020 12:49 AM

Re: Latex Help
I tried \mu \pi \lambda but didn't put the extra brackets around them. Sooo, close.

Thank you, nwr.

Factio Republicana delenda est.

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nwr
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Joined: 08-08-2005
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 Message 589 of 650 (876242) 05-15-2020 8:30 AM Reply to: Message 588 by AZPaul305-15-2020 5:40 AM

Re: Latex Help
You can use: \mu

You cannot use: \muv

Maybe this would work: \mu v
but using extra braces avoids the problem.

Fundamentalism - the anti-American, anti-Christian branch of American Christianity

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dwise1
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 Message 590 of 650 (876252) 05-15-2020 3:55 PM Reply to: Message 587 by nwr05-15-2020 12:49 AM

Re: Latex Help
Does the forum have help on Latex syntax with examples? Basically, where are the resources to learn how to use it?

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nwr
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From: Geneva, Illinois
Joined: 08-08-2005
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 Message 591 of 650 (876253) 05-15-2020 4:05 PM Reply to: Message 590 by dwise105-15-2020 3:55 PM

Re: Latex Help
I learned mostly from the book (the Leslie Lamport book). The "La" part of "LaTeX" is from "Lamport". It is probably easier to look up online documentation.

LaTeX Documentation

Fundamentalism - the anti-American, anti-Christian branch of American Christianity

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dwise1
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 (1)
 Message 592 of 650 (876255) 05-15-2020 4:20 PM Reply to: Message 591 by nwr05-15-2020 4:05 PM

Re: Latex Help
OK, that's not helpful. Though I did have to chuckle at the title for French documentation, "Tout ce que vous avez toujours voulu savoir sur LaTeX", that left out the "mais aviez peur de demander."

Just "how would one use it on this forum?", not "how would I typeset an entire physics book using nroff?"

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nwr
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Joined: 08-08-2005
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 Message 593 of 650 (876256) 05-15-2020 4:44 PM Reply to: Message 592 by dwise105-15-2020 4:20 PM

Re: Latex Help
Perhaps this is more useful:

LaTeX Mathematics

Fundamentalism - the anti-American, anti-Christian branch of American Christianity

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 Message 594 of 650 (876257) 05-15-2020 5:51 PM Reply to: Message 593 by nwr05-15-2020 4:44 PM

Re: Latex Help
The forum's help for the [latex] dBCode can be found at Latex Help. It includes a link to NASA's Latex Help.

 -- Percy EvC Forum Director

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dwise1
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 Message 595 of 650 (876258) 05-15-2020 6:06 PM Reply to: Message 593 by nwr05-15-2020 4:44 PM

Re: Latex Help

Is this just an nroff and dBCodes thang, or can it be used in HTML?

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nwr
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Posts: 5794
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 4.7

 Message 596 of 650 (876260) 05-15-2020 9:09 PM Reply to: Message 595 by dwise105-15-2020 6:06 PM

Re: Latex Help
 Is this just an nroff and dBCodes thang, or can it be used in HTML?

It's a typesetting system oriented toward the use of mathematics. It existed before dBcodes or HTML ever existed.

There is a "latex2html" command for linux. Also wordpress has a latex plugin for its blog software. And I think Google's "blogspot" has something similar.

What typically happens with "latex2html", with the wordpress plugin and with dBcodes support, is that those use just the mathematics rendering part of latex. They use latex to typeset a mathematical formula, then make an image of that. Then the display the image in the web page. Percy would know more about that part, since he implemented it for his forum software.

Fundamentalism - the anti-American, anti-Christian branch of American Christianity

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RAZD
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Posts: 20714
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Joined: 03-14-2004

 Message 597 of 650 (876273) 05-16-2020 10:54 AM Reply to: Message 596 by nwr05-15-2020 9:09 PM

Re: Latex Help
I noticed when copying formulas from wiki that they use latex, but not quite the same, so it needs some interpretation.

Enjoy

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dwise1
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 Message 598 of 650 (876285) 05-16-2020 12:47 PM Reply to: Message 596 by nwr05-15-2020 9:09 PM

Re: Latex Help
Google'ing about, I found an example which I did get to work on a local HTML file using Chrome.

quote:
<script type="text/javascript" src="http://latex.codecogs.com/latexit.js"></script>

Then in the page body, add something like:

quote:
<div lang="latex">
\frac{1+sin(x)}{y}
</div>

And you get:

OK, that seems to work.

However, I found that on the CodeCogs site. I don't know them and here I am pulling one of their scripts into my site without knowing what all it does. I also don't know which browsers they support or whether their support would continue.

So some way to generate an image of the formula would probably be best unless there is some generally available way to support latex in HTML.

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dwise1
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 Message 599 of 650 (880500) 08-06-2020 10:01 PM

I've been working on a couple web pages about switching from the US Customary System of measurements (AKA "Imperial") to the metric system. I'm currently working on the page that offers some short-cut methods to approximate conversion but for the purpose of developing a feel for how much these measurements are. Part of that approach employs a Boy Scout skill we were taught in the 1960's in which we use parts of our body (no, not that part) to estimate lengths.

In that section, I'm including some methods from a German constellation atlas which estimate degrees of separation of sky objects with your hand held out at arm's length; from my page's draft:

quote:
With your arm extended out before you (distance = 50 cm, about 20 inches):
• thumb width = 2.5 degrees
• closed fist minus thumb = 9 degrees
• outspread hand, thumb to pinky = 22 degrees

I should also include what I had been taught in my youth, that you can estimate how long before the sun sets with the same method, but each finger of your hand represents 15 minutes.

My question is regarding an instrument I've seen in medieval woodcut prints which was used to measure angles of separation in the sky. Here is the description in my current draft:

quote:
There was a Medieval astronomical instrument that I've seen in illustrations but don't know the name of. It was based on the same principles just described to measure the angle between objects. It was a piece of wood (about 1×1 and one yard long) that may have been graduated (ie, be marked with measurement lines). Towards the opposite end was a short cross member. Either the cross member was fixed and was itself graduated, or it could be moved along the long member until the objects being measured were at its ends. The user would place one end near his eye and sight down the length, adjusting the cross member (or sighting measurements on the cross member, depending on which design was used) to sight the objects being measured, and then read off the angle. You could use trigonometry to calculate what its dimensions would have be.

Is anybody familiar with that instrument and knows what it was called as well as just how it did actually work?

 Replies to this message: Message 600 by Pollux, posted 08-06-2020 10:51 PM dwise1 has responded Message 601 by nwr, posted 08-06-2020 11:22 PM dwise1 has responded

Pollux
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 Message 600 of 650 (880501) 08-06-2020 10:51 PM Reply to: Message 599 by dwise108-06-2020 10:01 PM

It sounds like a Davis quadrant.
Wikipedia has an article on it

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