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bug#13580: 24.2.92; regression in calc-convert-units
From: |
Eli Zaretskii |
Subject: |
bug#13580: 24.2.92; regression in calc-convert-units |
Date: |
Fri, 08 Feb 2013 10:33:59 +0200 |
> From: Jay Belanger <address@hidden>
> Date: Thu, 07 Feb 2013 15:11:58 -0600
>
> I've been consistently talking about units, not dimensions; I have given
> no interpretation of "dimensions" vs "units". The expression above has
> no units when simplified; that's a pretty straightforward statement.
He is talking about this (see
http://en.wikipedia.org/wiki/Dimensionless_quantity):
In dimensional analysis, a dimensionless quantity or quantity of
dimension one is a quantity without an associated physical
dimension. It is thus a "pure" number, and as such always has a
dimension of 1. [...]
Even though a dimensionless quantity has no physical dimension
associated with it, it can still have dimensionless units. To show the
quantity being measured (for example mass fraction or mole fraction),
it is sometimes helpful to use the same units in both the numerator
and denominator (kg/kg or mol/mol). The quantity may also be given as
a ratio of two different units that have the same dimension (for
instance, light years over meters). This may be the case when
calculating slopes in graphs, or when making unit conversions. Such
notation does not indicate the presence of physical dimensions, and is
purely a notational convention. Other common dimensionless units are
% (= 0.01), ‰ (= 0.001), [...] and angle units (degrees, radians, grad).
Therefore, "dimensionless" and "unitless" is not the same, and you see
above prominent examples of such dimensionless units.
IOW, removing dimensions of an expression as part of simplifying it
might sometimes lose information. E.g., dividing the length of a
circular arc by its radius will give you m/m, but the natural units of
this are radians or degrees, not lack of units, and talking about
"unitless" in this case might make little sense to a user who _knows_
she is computing an angle.
- bug#13580: 24.2.92; regression in calc-convert-units, (continued)
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/07
- bug#13580: 24.2.92; regression in calc-convert-units, Roland Winkler, 2013/02/07
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/07
- bug#13580: 24.2.92; regression in calc-convert-units, Glenn Morris, 2013/02/07
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/07
- bug#13580: 24.2.92; regression in calc-convert-units, Glenn Morris, 2013/02/07
- bug#13580: 24.2.92; regression in calc-convert-units, Roland Winkler, 2013/02/07
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/07
- bug#13580: 24.2.92; regression in calc-convert-units, Roland Winkler, 2013/02/07
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/07
- bug#13580: 24.2.92; regression in calc-convert-units,
Eli Zaretskii <=
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/08
- bug#13580: 24.2.92; regression in calc-convert-units, Eli Zaretskii, 2013/02/08
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/08
- bug#13580: 24.2.92; regression in calc-convert-units, Roland Winkler, 2013/02/08
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/09
- bug#13580: 24.2.92; regression in calc-convert-units, Roland Winkler, 2013/02/09
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/09
- bug#13580: 24.2.92; regression in calc-convert-units, Roland Winkler, 2013/02/09
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/09
- bug#13580: 24.2.92; regression in calc-convert-units, Jay Belanger, 2013/02/08