## Mathematica Memos

Posted May21-12 at 04:24 PM by ChristinaJ

Some basic Mathematica info, mostly to stop myself having to continually research things that I should already know. Basic syntax to start.

(*comment*) code comments should be between (*
“string”a string is defined by quotation marks.
a is an assignment.
2*10^5 standard form (replaces the usual 2e5).
esc phi esc greek letter phi.
Sin[0] functions begin with a capital letter with their arguments in square brackets.
{x1, x2, x3} list of variables....
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## How to post a question at Physics Forums

Posted May18-12 at 01:41 PM by Redbelly98
Updated May21-12 at 03:37 PM by Redbelly98

If you are new to Physics Forums and want to post a question, you need to start a new forum discussion thread, known simply as a "thread". To do that, read the following instructions . . . and be sure to read the part at the end if your question is related to schoolwork or to solving any textbook-style problem, even if it's for independent study.

How to start a forum discussion thread.

To post a question -- or to start any new discussion at Physics Forums...
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## Relativity and semantics

Posted May16-12 at 04:01 PM by Saw (Einstein, Cinderella and the slipper)

Dalespam recently brought up an interesting semantic issue. What is the meaning of “relative” versus “absolute”? I did not have time to intervene in that thread but the subject links well with the musings of this Blog.

Obviously “relative” is what is defined “in relation with” or by comparison with another object, but in the context of Special Relativity this may mean three different things:

(a) That a measurement (of time or space) is made from and hence with regard...
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$$R = \frac{\sigma(e^+ P^+ \rightarrow C)}{\sigma(e^+ P^+ \rightarrow \bar{\nu}_e)}$$