Module: Units

Includes:
UseBlocks
Defined in:
lib/units/math.rb,
lib/units-system.rb,
lib/units/system.rb,
lib/units/measure.rb,
lib/units/prefixes.rb,
lib/units/definitions.rb

Defined Under Namespace

Modules: Math, System, UseBlocks Classes: Measure, UnitDefinition

Constant Summary collapse

UNITS =

Hash.new{|h,k| h=UnitDefinition.new()}

{}
SI_UNITS = 
{}
PREFIXES = 
{
  :y=>[1E-24, 'yocto'],
  :z=>[1E-21, 'zepto'],
  :a=>[1E-18, 'atto'],
  :f=>[1E-15, 'femto'],
  :p=>[1E-12, 'pico'],
  :n=>[1E-09, 'nano'],
  :"\302\265"=>[1E-06, 'micro'],
  :"u"=>[1E-06, 'micro'],
  :m=>[1E-03, 'milli'],
  :c=>[1E-02, 'centi'],
  :d=>[1E-01, 'deci'],
  :da=>[1E1, 'deca'],
  :h=>[1E02, 'hecto'],
  :k=>[1E03, 'kilo'],
  :M=>[1E06, 'mega'],
  :G=>[1E09, 'giga'],
  :T=>[1E12, 'tera'],
  :P=>[1E15, 'peta'],
  :E=>[1E18, 'exa'],
  :Z=>[1E21, 'zetta'],
  :Y=>[1E24, 'yotta']
}

Class Method Summary collapse

Methods included from UseBlocks

append_features

Class Method Details

.conversion_bias(from, to) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'lib/units/system.rb', line 177

def self.conversion_bias(from, to)
  from_u = unit(from)
  to_u = unit(to)
  raise ArgumentError,"Inconsistent Units (#{from}, #{to})" if from_u.dim!=to_u.dim
  factor = from_u.factor/to_u.factor
  (from_u.bias||0)*factor - (to_u.bias||0)
end

.conversion_factor(from, to) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'lib/units/system.rb', line 170

def self.conversion_factor(from, to)
  from_u = unit(from)
  to_u = unit(to)
  raise ArgumentError,"Inconsistent Units (#{from}, #{to})" if from_u.dim!=to_u.dim
  from_u.factor/to_u.factor
end

.define(unit_symbol, name, *args) ⇒ Object

Define new units. Define a base unit (with a factor for conversion to SI units)

Units.define :unit_symbol, 'unit-name', :quantity, si_units_per_this_unit

Define a unit in terms or another (valid for base or derived units)

Units.define :unit_symbol, 'unit-name', value, :in_units

Define a base unit as a measure-expression

Units.define :unit_symbol, 'unit_name', u{...}

Define a derived unit as a measure-expression

Units.define :unit_symbol, 'unit_name', :quantity, u{...}

For base dimensions the SI unit for a quantity must also be stablished with Unit.si_units; for derived units, SI units are automatically taken to be the first define unit of the quantity with unitary value in SI base units.



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# File 'lib/units/system.rb', line 102

def self.define(unit_symbol, name, *args)
  eqhivalence = nil
  si_unit = false
  bias = nil
  if args.first.kind_of?(Symbol)
    dim = args.shift
    if args.first.kind_of?(Numeric)
      # simple units
      factor = args.shift
      factor_units = args.shift
      if factor_units
        ud = unit(factor_units)
        if ud.dim != dim
          raise ArgumentError, "Inconsistent units #{factor_units} in definition of #{unit_symbol}"
        end
        # maybe it was not simple after all...
        equivalence = factor*ud.decomposition if ud.decomposition
        factor *= ud.factor
      end
      # si_unit = (factor==1.0) # to save si_units definitions # TODO: tolerance?
    else
      # compound unit
      equivalence = args.shift
      factor = equivalence.to_si.magnitude
      si_unit = (factor==1.0) # TODO: tolerance?
      if equivalence.units.empty?
        # dimensionless compound dimension... (special case for angular units)
        equivalence = nil
      end
    end
  elsif args.first.kind_of?(Numeric)
    # unit define in terms of other unit
    factor = args.shift
    factor_units = args.shift
    u = unit(factor_units)
    dim = u.dim
    equivalence = factor*u.decomposition if u.decomposition
    factor *= u.factor
    bias = args.shift
  else
    # unit defined from a measure expression; the dimension must be already known or defined
    # here (as as symbol preceding the expression).
    definition = args.shift
    dim = definition.dimension
    raise ArgumentError,"To define a new compound unit a dimension must be specified" unless dim
    equivalence = definition
    factor = definition.to_si.magnitude
    # si_unit = (factor==1.0) # to save si_units definitions # TODO: tolerance?
  end
  unit_def = UnitDefinition.new(dim, factor, name, equivalence, bias)
  if UNITS.has_key?(unit_symbol)
    raise "Redefinition of #{unit_symbol} as #{unit_def} (previously defined as #{UNITS[unit_symbol]})"
  end
  UNITS[unit_symbol] = unit_def
  System.define unit_symbol
  Units.si_units unit_def.dim, unit_symbol if si_unit && !SI_UNITS.has_key?(unit_def.dim)
end

.dimension(u) ⇒ Object 



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# File 'lib/units/system.rb', line 166

def self.dimension(u)
  unit(u).dim
end

.Measure(*args) ⇒ Object

Measure



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# File 'lib/units/measure.rb', line 275

def Measure(*args)
  Measure[*args]
end

.prefix_factor(prefix) ⇒ Object 



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# File 'lib/units/prefixes.rb', line 29

def self.prefix_factor(prefix)
  pd = PREFIXES[prefix.to_sym]
  pd && pd.first
end

.prefix_factor_and_name(prefix) ⇒ Object 



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# File 'lib/units/prefixes.rb', line 39

def self.prefix_factor_and_name(prefix)
  PREFIXES[prefix]
end

.prefix_name(prefix) ⇒ Object 



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# File 'lib/units/prefixes.rb', line 34

def self.prefix_name(prefix)
  pd = PREFIXES[prefix.to_sym]
  pd && pd.last
end

.si_units(dim, unit) ⇒ Object 



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# File 'lib/units/system.rb', line 162

def self.si_units(dim, unit)
  SI_UNITS[dim] = unit
end

.u ⇒ Object

Units::System



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# File 'lib/units/system.rb', line 54

def units(string=nil, &blk)
  if string
    if blk
      raise ArgumentError, "wrong number of arguments (1 for 0)"
    else
      Units::System.class_eval(string)
    end
  else
    Units::System.class_eval(&blk)
  end
end

.unit(unit_symbol) ⇒ Object

get unit definition

Raises:

  • (ArgumentError) 


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# File 'lib/units/system.rb', line 62

def self.unit(unit_symbol)
  ud = UNITS[unit_symbol]
  if ud.nil?
    factor = 1.0
    if factor_name = PREFIXES[unit_symbol]
      ud = UnitDefinition.new(nil, *factor_name)
    else
      u = unit_symbol.to_s
      PREFIXES.each_pair do |prefix, (f,name)|
        prefix = prefix.to_s
        if u[0...prefix.length] == prefix
          factor = f
          ud = UNITS[u[prefix.length..-1].to_sym]
          if ud
            ud = ud.dup
            ud.name = "#{name}#{ud.name}"
            break
          end
        end
      end
    end
    ud.factor *= factor if ud
    ud.decomposition *= factor if ud && ud.decomposition
  end
  raise ArgumentError,"Invalid Units #{unit_symbol}" unless ud
  ud
end

.unit_descr(u, long = false, mult = 1) ⇒ Object 



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# File 'lib/units/system.rb', line 191

def self.unit_descr(u, long=false, mult=1)
  if long
    u = unit_name(u)
    if mult!=1
      case mult
      when 2
        "squared #{u}"
      when 3
        "cubed #{u}"
      else
        "#{u} to the #{mult} power"
      end
    else
      u
    end
  else
    if mult!=1
      "#{u}**#{mult}"
    else
      u.to_s
    end
  end
end

.unit_name(u) ⇒ Object

simple unit name



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# File 'lib/units/system.rb', line 186

def self.unit_name(u)
  uinfo = Units.unit(u)
  uinfo && uinfo.name
end

.units(string = nil, &blk) ⇒ Object

Units::System



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# File 'lib/units/system.rb', line 43

def units(string=nil, &blk)
  if string
    if blk
      raise ArgumentError, "wrong number of arguments (1 for 0)"
    else
      Units::System.class_eval(string)
    end
  else
    Units::System.class_eval(&blk)
  end
end

.units_descr(units, long = false) ⇒ Object 



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# File 'lib/units/system.rb', line 215

def self.units_descr(units, long=false)
  units = units.values.sort_by{|u,m| -m}
  pos_units = units.select{|u| u.last>0}
  neg_units = units.select{|u| u.last<0}
  times = long ? " " : "*"
  num = pos_units.map{|u,m| unit_descr(u,long,m)}.join(times)
  num = "(#{num})" if pos_units.size>1 && !neg_units.empty? && !long
  den = neg_units.map{|u,m| unit_descr(u,long,-m)}.join("*")
  den = "(#{den})" if neg_units.size>1 && !long
  if pos_units.empty?
    u_descr = "1/#{den}"
  elsif neg_units.empty?
    u_descr = num
  else
    connector = long ? " per " : "/"
    u_descr = "#{num}#{connector}#{den}"
  end
  u_descr
end