Arjen Markus (17 june 2004) Here is a first almost trivial example of how Tcl could be used to facilitate certain physical computations ... I hope I can make this grow into a more serious package ;)
AM (18 june 2004) One thing that might be very useful in such a package: a short explanation of the various procedures and constants, especially if you are using it interactively. BTW, the unit converter is a much better way to achieve the unit conversions I haphazardly implemented here.
# physparam.tcl --
# Musings over the question of units in phyiscal computations
#
# Simple example:
# Conversion of temperature to absolute temperature
# In many formulas you need to specify the absolute temperature
# rather than the temperature most people are used to (degrees
# centigrade or the infamous degrees Fahrenheit).
# Mistakes are easily made ... so include the unit in the value.
#
#
# physics --
# Namespace for the physical computations
#
namespace eval ::physics {
#
# Add common constants etc.
#
namespace export abs_temperature wien_wavelength
}
# Conversions --
# Set of conversion procedures
#
proc ::physics::Conv_K_K {t} {return $t}
proc ::physics::Conv_oC_K {t} {expr {$t+273.15}}
proc ::physics::Conv_oF_K {t} {Conv_oC_K [Conv_oF_oC $t]}
proc ::physics::Conv_oF_oC {t} {expr {5.0*$t/9.0+32.0}}
# abs_temperature --
# Return the absolute temperature
#
# Arguments:
# temp (Relative) temperature
#
# Result:
# The temperature in kelvin (no capital, there was only one
# lord Kelvin, AFAIK :)
#
proc ::physics::abs_temperature {temp} {
if { [llength $temp] == 2 } {
set temp [Conv_[lindex $temp 1]_K [lindex $temp 0]]
}
list $temp K
}
# wien_wavelength --
# Return the wave length at which a perfect black body emits most
# energy, given the temperature
#
# Arguments:
# temp (Relative) temperature
#
# Result:
# The wave length in micrometers (um)
#
proc ::physics::wien_wavelength {temp} {
list [expr {2898.0/[lindex [abs_temperature $temp] 0]}] um
}
# main --
# A simple demonstration
#
namespace import ::physics::*
puts "20 degrees centigrade = [abs_temperature {20 oC}]"
puts "50 degrees Fahrenheit = [abs_temperature {50 oF}]"
puts "At 20 degrees centigrade a black body emits most
energy with a wave length of [wien_wavelength {20 oC}]"How does this relate to Unit converter and Unit math ?
AM Closely - though my intentions are different than "merely" converting from one unit to another. I want to make the unit an integral part of the quantity's value. This way I can use such quantities in all kinds of simple computations (that is, computations that do not require the solution of partial differential equations and the like).
Something like: I want to know the density of sea water at a given temperature and salinity - so use one of the constitutional equations that people have developed.
[ Category Physics ]