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Assume v. Presume

I have only just read the last 2 pages of this thread, so forgive me if I repeat something someone else has said...

As an engineer (as in MIET) and with not necessarily any other backup than the opinion I'm about to state...

I always think of a (maths not chemical) formula as something that is a well-known given - e.g. double angle formula such as cos(x+y) = cos(x)cos(y)-sin(x)sin(y).
Equation?
d²E/dx²+d²E/dy²=μεd²E/dt²
(incidentally I would read that as d 2 e by d x squared!)

But I might now say substitute the expression 1/(με)=c² gives ...
- I think I may also use the terms substitute the equation. (so equation/expression interchangable?)
I hope that adds to the confusion (and don't rely on my maths for solving electromag problems as it may be wrong and I was having problems inputting them).
 
Mike0001 said:
ROFL @Black Hole That's square d e by square d x to you.
Click to expand...
:D To be fair, this is not the same as 6m² where there may be a debate whether you mean 6 metres square (6m x 6m -no) or 6 square metres (eg 2m x 3m -maybe) or 6 metres-squared (also 2m x 3m - maybe). Just my opinion - the "squared" rather than "square" makes the difference. :confused:
 
EEPhil said:
:D To be fair, this is not the same as 6m² where there may be a debate whether you mean 6 metres square (6m x 6m -no) or 6 square metres (eg 2m x 3m -maybe) or 6 metres-squared (also 2m x 3m - maybe).
Click to expand...


If we intended six square metres we would write 6 ²m. :p

Anyway, with more complex dimensions involving several powers of metres, seconds, grams, nobody is going to start switching the order of the unit and exponent. What do you say if it has a m⁷ or an s⁻⁵ in it?

No, consistency is important.

EEPhil said:
Just my opinion - the "squared" rather than "square" makes the difference. :confused:
Click to expand...

Also, we would say a square with side 6 metres rather than the ambiguous a six metre square. (Or six metres squared.)
 
Trev said:
Except that convention has the superscript power indicator after the units of measurements. So 6m ² is unambiguously six square metres not six metres square.
Click to expand...

I was just saying, we should say it how it is written. (Other reasons added in a previous post.) Anyway, 6 square=36. QED
 
Mike0001 said:
@MikeSh Alt 0178 just converts this tab into a new tab for me! It used to work on old PCs but I guess loads of these Alt codes have been subverted now.
Click to expand...
Yes, I get that sort of effect if the Num Lock is OFF. But with it on it works fine (Windows 7). They don't work with the numbers above the QWERTY board , only the separate keypad - with Num Lock ON.
The codes are still given in Character Map, so I doubt they are subverted.

Mike0001 said:
Anyway, the characters you can get in Unicode are so limited, there isn't much point.
Click to expand...

The problem with going outside Unicode is when posting on forums, etc. 'Special' codes may either not work or appear as something quite different on other devices.
 
Black Hole said:
Sinful! In that case, you know the current skirmish but not the game.
Click to expand...
:oops:Pardon me for intruding. However, reading 1.5 years worth of semantic quibbling takes a long time. ;) (and I was trying to be fair to you by pointing out that my reading of an equation isn't the same arguing over m²/square-metres/metres-squared etc - but obviously I made a bodge of that!)

In reply to Mike0001, I would say (at least to myself) "metres-to-the-seventh" and "seconds-to-the-minus-five" (or 1 over seconds to the fifth).
In most of these things context and consistency are important. In an equation like d²E/dx²+d²E/dy²=μεd²E/dt² there really isn't any ambiguity as to what the square term means. In fact I don't think the ambiguity comes from the maths. I agree if you write 6m² there is no ambiguity. If you say 6 square metres there is.
 
EEPhil said:
I agree if you write 6m² there is no ambiguity. :oops:If you say 6 square metres there is.
Click to expand...



Totally agree on the first one. I would always say six metres squared for that reason.

Everyone knows the calculus notation is a load of bull, anyway, but we are stuck with it. Not such a load of bull as tensor notation, though, or that abomination bra-ket notation that uses <a| and |b>. Maths is full of poor choices of notation. The web compounds the problem by making it almost impossible even to use any notations whatsoever unless you have a browser like Firefox that can render MathML and also you are not in a forum which disallows any XHTML markup.

As for negative superscripts, well, Character Map in Windoze was no help at all! I had to resort to a quick copy and paste from

http://www.alanwood.net/unicode/superscripts_and_subscripts.html
 
MikeSh said:
The problem with going outside Unicode is when posting on forums, etc. 'Special' codes may either not work or appear as something quite different on other devices.
Click to expand...

It was a criticism of what was included in Unicode, not a wish to use a special font only available on one platform. MathML is capable of representing just about any expression. In a forum, you are stuck with the Unicode characters, which, incidentally, also get messed up on other platforms that don't have the appropriate glyphs.
 
Black Hole said:
I suggest you go to the builders merchants and try your phrasiology out there.
Click to expand...
Hmm. I was going to make a point about buying carpet. "I want 6 square metres of carpet", but you'd have to be more precise. "I want a piece of carpet 2m by 3m". Or, in the case of the builders merchants "I want a piece of plywood 2 x 3 metres". Surely you wouldn't ask for 6 square metres or 6 metres squared. You might ask for 6 metres square - meaning 6 x 6. But you wouldn't write this down as 6m². Wouldn't you write this as 6m x 6m - or just maybe 6x6m if you're lazy?
 
In everyday life you often have a choice of being accurate/correct/pedantic OR being understood. The latter usually means keeping all sizes as single dimensions :)
 
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