Previous: Introduction to physical_constants, Up: ezunits [Contents][Index]
The dimensional quantity operator.
An expression \(a ` b\) represents a dimensional quantity,
with a indicating a nondimensional quantity and b indicating the dimensional units.
A symbol can be used as a unit without declaring it as such;
unit symbols need not have any special properties.
The quantity and unit of an expression \(a ` b\) can
be extracted by the qty and units functions, respectively.
Arithmetic operations on dimensional quantities are carried out by conventional rules for such operations.
y is nondimensional.
ezunits does not require that units in a sum have the same dimensions;
such terms are not added together, and no error is reported.
load ("ezunits") enables this operator.
Examples:
SI (Systeme Internationale) units.
(%i1) load ("ezunits")$
(%i2) foo : 10 ` m;
(%o2) 10 ` m
(%i3) qty (foo);
(%o3) 10
(%i4) units (foo);
(%o4) m
(%i5) dimensions (foo);
(%o5) length
"Customary" units.
(%i1) load ("ezunits")$
(%i2) bar : x ` acre;
(%o2) x ` acre
(%i3) dimensions (bar);
2
(%o3) length
(%i4) fundamental_units (bar);
2
(%o4) m
Units ad hoc.
(%i1) load ("ezunits")$
(%i2) baz : 3 ` sheep + 8 ` goat + 1 ` horse;
(%o2) 8 ` goat + 3 ` sheep + 1 ` horse
(%i3) subst ([sheep = 3*goat, horse = 10*goat], baz);
(%o3) 27 ` goat
(%i4) baz2 : 1000`gallon/fortnight;
gallon
(%o4) 1000 ` ---------
fortnight
(%i5) subst (fortnight = 14*day, baz2);
500 gallon
(%o5) --- ` ------
7 day
Arithmetic operations on dimensional quantities.
(%i1) load ("ezunits")$
(%i2) 100 ` kg + 200 ` kg;
(%o2) 300 ` kg
(%i3) 100 ` m^3 - 100 ` m^3;
3
(%o3) 0 ` m
(%i4) (10 ` kg) * (17 ` m/s^2);
kg m
(%o4) 170 ` ----
2
s
(%i5) (x ` m) / (y ` s);
x m
(%o5) - ` -
y s
(%i6) (a ` m)^2;
2 2
(%o6) a ` m
The unit conversion operator.
An expression a ` b `` c converts from unit b to unit c.
ezunits has built-in conversions for SI base units,
SI derived units, and some non-SI units.
Unit conversions not already known to ezunits can be declared.
The unit conversions known to ezunits are specified by the
global variable known_unit_conversions,
which comprises built-in and user-defined conversions.
Conversions for products, quotients, and powers of units are
derived from the set of known unit conversions.
There is no preferred system for display of units;
input units are not converted to other units
unless conversion is explicitly indicated.
ezunits does not attempt to simplify units by prefixes
(milli-, centi-, deci-, etc)
unless such conversion is explicitly indicated.
load ("ezunits") enables this operator.
Examples:
The set of known unit conversions.
(%i1) load ("ezunits")$
(%i2) display2d : false$
(%i3) known_unit_conversions;
(%o3) {acre = 4840*yard^2,Btu = 1055*J,cfm = feet^3/minute,
cm = m/100,day = 86400*s,feet = 381*m/1250,ft = feet,
g = kg/1000,gallon = 757*l/200,GHz = 1000000000*Hz,
GOhm = 1000000000*Ohm,GPa = 1000000000*Pa,
GWb = 1000000000*Wb,Gg = 1000000*kg,Gm = 1000000000*m,
Gmol = 1000000*mol,Gs = 1000000000*s,ha = hectare,
hectare = 100*m^2,hour = 3600*s,Hz = 1/s,inch = feet/12,
km = 1000*m,kmol = 1000*mol,ks = 1000*s,l = liter,
lbf = pound_force,lbm = pound_mass,liter = m^3/1000,
metric_ton = Mg,mg = kg/1000000,MHz = 1000000*Hz,
microgram = kg/1000000000,micrometer = m/1000000,
micron = micrometer,microsecond = s/1000000,
mile = 5280*feet,minute = 60*s,mm = m/1000,
mmol = mol/1000,month = 2629800*s,MOhm = 1000000*Ohm,
MPa = 1000000*Pa,ms = s/1000,MWb = 1000000*Wb,
Mg = 1000*kg,Mm = 1000000*m,Mmol = 1000000000*mol,
Ms = 1000000*s,ns = s/1000000000,ounce = pound_mass/16,
oz = ounce,Ohm = s*J/C^2,
pound_force = 32*ft*pound_mass/s^2,
pound_mass = 200*kg/441,psi = pound_force/inch^2,
Pa = N/m^2,week = 604800*s,Wb = J/A,yard = 3*feet,
year = 31557600*s,C = s*A,F = C^2/J,GA = 1000000000*A,
GC = 1000000000*C,GF = 1000000000*F,GH = 1000000000*H,
GJ = 1000000000*J,GK = 1000000000*K,GN = 1000000000*N,
GS = 1000000000*S,GT = 1000000000*T,GV = 1000000000*V,
GW = 1000000000*W,H = J/A^2,J = m*N,kA = 1000*A,
kC = 1000*C,kF = 1000*F,kH = 1000*H,kHz = 1000*Hz,
kJ = 1000*J,kK = 1000*K,kN = 1000*N,kOhm = 1000*Ohm,
kPa = 1000*Pa,kS = 1000*S,kT = 1000*T,kV = 1000*V,
kW = 1000*W,kWb = 1000*Wb,mA = A/1000,mC = C/1000,
mF = F/1000,mH = H/1000,mHz = Hz/1000,mJ = J/1000,
mK = K/1000,mN = N/1000,mOhm = Ohm/1000,mPa = Pa/1000,
mS = S/1000,mT = T/1000,mV = V/1000,mW = W/1000,
mWb = Wb/1000,MA = 1000000*A,MC = 1000000*C,
MF = 1000000*F,MH = 1000000*H,MJ = 1000000*J,
MK = 1000000*K,MN = 1000000*N,MS = 1000000*S,
MT = 1000000*T,MV = 1000000*V,MW = 1000000*W,
N = kg*m/s^2,R = 5*K/9,S = 1/Ohm,T = J/(m^2*A),V = J/C,
W = J/s}
Elementary unit conversions.
(%i1) load ("ezunits")$
(%i2) 1 ` ft `` m;
Computing conversions to base units; may take a moment.
381
(%o2) ---- ` m
1250
(%i3) %, numer;
(%o3) 0.3048 ` m
(%i4) 1 ` kg `` lbm;
441
(%o4) --- ` lbm
200
(%i5) %, numer;
(%o5) 2.205 ` lbm
(%i6) 1 ` W `` Btu/hour;
720 Btu
(%o6) --- ` ----
211 hour
(%i7) %, numer;
Btu
(%o7) 3.412322274881517 ` ----
hour
(%i8) 100 ` degC `` degF;
(%o8) 212 ` degF
(%i9) -40 ` degF `` degC;
(%o9) (- 40) ` degC
(%i10) 1 ` acre*ft `` m^3;
60228605349 3
(%o10) ----------- ` m
48828125
(%i11) %, numer;
3
(%o11) 1233.48183754752 ` m
Coercing quantities in feet and meters to one or the other.
(%i1) load ("ezunits")$
(%i2) 100 ` m + 100 ` ft;
(%o2) 100 ` m + 100 ` ft
(%i3) (100 ` m + 100 ` ft) `` ft;
Computing conversions to base units; may take a moment.
163100
(%o3) ------ ` ft
381
(%i4) %, numer;
(%o4) 428.0839895013123 ` ft
(%i5) (100 ` m + 100 ` ft) `` m;
3262
(%o5) ---- ` m
25
(%i6) %, numer;
(%o6) 130.48 ` m
Dimensional analysis to find fundamental dimensions and fundamental units.
(%i1) load ("ezunits")$
(%i2) foo : 1 ` acre * ft;
(%o2) 1 ` acre ft
(%i3) dimensions (foo);
3
(%o3) length
(%i4) fundamental_units (foo);
3
(%o4) m
(%i5) foo `` m^3;
Computing conversions to base units; may take a moment.
60228605349 3
(%o5) ----------- ` m
48828125
(%i6) %, numer;
3
(%o6) 1233.48183754752 ` m
Declared unit conversions.
(%i1) load ("ezunits")$
(%i2) declare_unit_conversion (MMBtu = 10^6*Btu, kW = 1000*W);
(%o2) done
(%i3) declare_unit_conversion (kWh = kW*hour, MWh = 1000*kWh,
bell = 1800*s);
(%o3) done
(%i4) 1 ` kW*s `` MWh;
Computing conversions to base units; may take a moment.
1
(%o4) ------- ` MWh
3600000
(%i5) 1 ` kW/m^2 `` MMBtu/bell/ft^2;
1306449 MMBtu
(%o5) ---------- ` --------
8242187500 2
bell ft
Shows the value and the units of one of the constants declared by package
physical_constants, which includes a list of physical constants, or
of a new constant declared in package ezunits (see
declare_constvalue).
Note that constant values as recognized by constvalue
are separate from values declared by numerval and
recognized by constantp.
Example:
(%i1) load ("physical_constants")$
(%i2) constvalue (%G);
3
m
(%o2) 6.67428 ` -----
2
kg s
(%i3) get ('%G, 'description);
(%o3) Newtonian constant of gravitation
Declares the value of a constant to be used in package ezunits. This
function should be loaded with load ("ezunits").
Example:
(%i1) load ("ezunits")$
(%i2) declare_constvalue (FOO, 100 ` lbm / acre);
lbm
(%o2) 100 ` ----
acre
(%i3) FOO * (50 ` acre);
(%o3) 50 FOO ` acre
(%i4) constvalue (%);
(%o4) 5000 ` lbm
Reverts the effect of declare_constvalue. This function should be
loaded with load ("ezunits").
Returns the units of a dimensional quantity x, or returns 1 if x is nondimensional.
x may be a literal dimensional expression \(a ` b\),
a symbol with declared units via declare_units,
or an expression containing either or both of those.
This function should be loaded with load ("ezunits").
Example:
(%i1) load ("ezunits")$
(%i2) foo : 100 ` kg;
(%o2) 100 ` kg
(%i3) bar : x ` m/s;
m
(%o3) x ` -
s
(%i4) units (foo);
(%o4) kg
(%i5) units (bar);
m
(%o5) -
s
(%i6) units (foo * bar);
kg m
(%o6) ----
s
(%i7) units (foo / bar);
kg s
(%o7) ----
m
(%i8) units (foo^2);
2
(%o8) kg
Declares that units should return units u for a,
where u is an expression. This function should be loaded with
load ("ezunits").
Example:
(%i1) load ("ezunits")$
(%i2) units (aa);
(%o2) 1
(%i3) declare_units (aa, J);
(%o3) J
(%i4) units (aa);
(%o4) J
(%i5) units (aa^2);
2
(%o5) J
(%i6) foo : 100 ` kg;
(%o6) 100 ` kg
(%i7) units (aa * foo);
(%o7) kg J
Returns the nondimensional part of a dimensional quantity x, or returns x if x is nondimensional. x may be a literal dimensional expression \(a ` b\), a symbol with declared quantity, or an expression containing either or both of those.
This function should be loaded with load ("ezunits").
Example:
(%i1) load ("ezunits")$
(%i2) foo : 100 ` kg;
(%o2) 100 ` kg
(%i3) qty (foo);
(%o3) 100
(%i4) bar : v ` m/s;
m
(%o4) v ` -
s
(%i5) foo * bar;
kg m
(%o5) 100 v ` ----
s
(%i6) qty (foo * bar);
(%o6) 100 v
Declares that qty should return x for symbol a, where
x is a nondimensional quantity. This function should be loaded
with load ("ezunits").
Example:
(%i1) load ("ezunits")$
(%i2) declare_qty (aa, xx);
(%o2) xx
(%i3) qty (aa);
(%o3) xx
(%i4) qty (aa^2);
2
(%o4) xx
(%i5) foo : 100 ` kg;
(%o5) 100 ` kg
(%i6) qty (aa * foo);
(%o6) 100 xx
Returns true if x is a literal dimensional expression,
a symbol declared dimensional,
or an expression in which the main operator is declared dimensional.
unitp returns false otherwise.
load ("ezunits") loads this function.
Examples:
unitp applied to a literal dimensional expression.
(%i1) load ("ezunits")$
(%i2) unitp (100 ` kg);
(%o2) true
unitp applied to a symbol declared dimensional.
(%i1) load ("ezunits")$
(%i2) unitp (foo);
(%o2) false
(%i3) declare (foo, dimensional);
(%o3) done
(%i4) unitp (foo);
(%o4) true
unitp applied to an expression in which the main operator is declared dimensional.
(%i1) load ("ezunits")$
(%i2) unitp (bar (x, y, z));
(%o2) false
(%i3) declare (bar, dimensional);
(%o3) done
(%i4) unitp (bar (x, y, z));
(%o4) true
Appends equations u = v, ... to the list of unit conversions known to the unit conversion operator ``. u and v are both multiplicative terms, in which any variables are units, or both literal dimensional expressions.
At present, it is necessary to express conversions such that the left-hand side of each equation is a simple unit (not a multiplicative expression) or a literal dimensional expression with the quantity equal to 1 and the unit being a simple unit. This limitation might be relaxed in future versions.
known_unit_conversions is the list of known unit conversions.
This function should be loaded with load ("ezunits").
Examples:
Unit conversions expressed by equations of multiplicative terms.
(%i1) load ("ezunits")$
(%i2) declare_unit_conversion (nautical_mile = 1852 * m,
fortnight = 14 * day);
(%o2) done
(%i3) 100 ` nautical_mile / fortnight `` m/s;
Computing conversions to base units; may take a moment.
463 m
(%o3) ---- ` -
3024 s
Unit conversions expressed by equations of literal dimensional expressions.
(%i1) load ("ezunits")$
(%i2) declare_unit_conversion (1 ` fluid_ounce = 2 ` tablespoon);
(%o2) done
(%i3) declare_unit_conversion (1 ` tablespoon = 3 ` teaspoon);
(%o3) done
(%i4) 15 ` fluid_ounce `` teaspoon;
Computing conversions to base units; may take a moment.
(%o4) 90 ` teaspoon
Declares a_1, ..., a_n to have dimensions d_1, ..., d_n, respectively.
Each a_k is a symbol or a list of symbols. If it is a list, then every symbol in a_k is declared to have dimension d_k.
load ("ezunits") loads these functions.
Examples:
(%i1) load ("ezunits") $
(%i2) declare_dimensions ([x, y, z], length, [t, u], time);
(%o2) done
(%i3) dimensions (y^2/u);
2
length
(%o3) -------
time
(%i4) fundamental_units (y^2/u);
0 errors, 0 warnings
2
m
(%o4) --
s
Reverts the effect of declare_dimensions. This function should be
loaded with load ("ezunits").
declare_fundamental_dimensions declares fundamental dimensions.
Symbols d_1, d_2, d_3, ... are appended to the list of
fundamental dimensions, if they are not already on the list.
remove_fundamental_dimensions reverts the effect of declare_fundamental_dimensions.
fundamental_dimensions is the list of fundamental dimensions.
By default, the list comprises several physical dimensions.
load ("ezunits") loads these functions.
Examples:
(%i1) load ("ezunits") $
(%i2) fundamental_dimensions;
(%o2) [length, mass, time, current, temperature, quantity]
(%i3) declare_fundamental_dimensions (money, cattle, happiness);
(%o3) done
(%i4) fundamental_dimensions;
(%o4) [length, mass, time, current, temperature, quantity,
money, cattle, happiness]
(%i5) remove_fundamental_dimensions (cattle, happiness);
(%o5) done
(%i6) fundamental_dimensions;
(%o6) [length, mass, time, current, temperature, quantity, money]
declare_fundamental_units declares u_1, ..., u_n
to have dimensions d_1, ..., d_n, respectively.
All arguments must be symbols.
After calling declare_fundamental_units,
dimensions(u_k) returns d_k for each argument u_1, ..., u_n,
and fundamental_units(d_k) returns u_k for each argument d_1, ..., d_n.
remove_fundamental_units reverts the effect of declare_fundamental_units.
load ("ezunits") loads these functions.
Examples:
(%i1) load ("ezunits") $
(%i2) declare_fundamental_dimensions (money, cattle, happiness);
(%o2) done
(%i3) declare_fundamental_units (dollar, money, goat, cattle,
smile, happiness);
(%o3) [dollar, goat, smile]
(%i4) dimensions (100 ` dollar/goat/km^2);
money
(%o4) --------------
2
cattle length
(%i5) dimensions (x ` smile/kg);
happiness
(%o5) ---------
mass
(%i6) fundamental_units (money*cattle/happiness);
0 errors, 0 warnings
dollar goat
(%o6) -----------
smile
dimensions returns the dimensions of the dimensional quantity x
as an expression comprising products and powers of base dimensions.
dimensions_as_list returns the dimensions of the dimensional quantity x
as a list, in which each element is an integer which indicates the power of the
corresponding base dimension in the dimensions of x.
load ("ezunits") loads these functions.
Examples:
(%i1) load ("ezunits")$
(%i2) dimensions (1000 ` kg*m^2/s^3);
2
length mass
(%o2) ------------
3
time
(%i3) declare_units (foo, acre*ft/hour);
acre ft
(%o3) -------
hour
(%i4) dimensions (foo);
3
length
(%o4) -------
time
(%i1) load ("ezunits")$
(%i2) fundamental_dimensions;
(%o2) [length, mass, time, charge, temperature, quantity]
(%i3) dimensions_as_list (1000 ` kg*m^2/s^3);
(%o3) [2, 1, - 3, 0, 0, 0]
(%i4) declare_units (foo, acre*ft/hour);
acre ft
(%o4) -------
hour
(%i5) dimensions_as_list (foo);
(%o5) [3, 0, - 1, 0, 0, 0]
fundamental_units(x) returns the units
associated with the fundamental dimensions of x.
as determined by dimensions(x).
x may be a literal dimensional expression \(a ` b\),
a symbol with declared units via declare_units,
or an expression containing either or both of those.
fundamental_units() returns the list of all known fundamental units,
as declared by declare_fundamental_units.
load ("ezunits") loads this function.
Examples:
(%i1) load ("ezunits")$
(%i2) fundamental_units ();
(%o2) [m, kg, s, A, K, mol]
(%i3) fundamental_units (100 ` mile/hour);
m
(%o3) -
s
(%i4) declare_units (aa, g/foot^2);
g
(%o4) -----
2
foot
(%i5) fundamental_units (aa);
kg
(%o5) --
2
m
Returns a basis for the dimensionless quantities which can be formed from a list L of dimensional quantities.
load ("ezunits") loads this function.
Examples:
(%i1) load ("ezunits") $
(%i2) dimensionless ([x ` m, y ` m/s, z ` s]);
0 errors, 0 warnings
0 errors, 0 warnings
y z
(%o2) [---]
x
Dimensionless quantities derived from fundamental physical quantities. Note that the first element on the list is proportional to the fine-structure constant.
(%i1) load ("ezunits") $
(%i2) load ("physical_constants") $
(%i3) dimensionless([%h_bar, %m_e, %m_P, %%e, %c, %e_0]);
0 errors, 0 warnings
0 errors, 0 warnings
2
%%e %m_e
(%o3) [--------------, ----]
%c %e_0 %h_bar %m_P
Finds exponents e_1, ..., e_n such that
dimension(expr) = dimension(v_1^e_1 ... v_n^e_n).
load ("ezunits") loads this function.
Examples:
Previous: Introduction to physical_constants, Up: ezunits [Contents][Index]