Temperature conversion

There are quite a number of temperature scales. For this task we will concentrate on 4 of the perhaps best-known ones: Kelvin, Celcius, Fahrenheit and Rankine.

The Celcius and Kelvin scales have the same magnitude, but different null points.

0 degrees Celcius corresponds to 273.15 kelvin.

0 kelvin is absolute zero.

The Fahrenheit and Rankine scales also have the same magnitude, but different null points.

0 degrees Fahrenheit corresponds to 459.67 degrees Rankine.

0 degrees Rankine is absolute zero.

The Celcius/Kelvin and Fahrenheit/Rankine scales have a ratio of 5 : 9.

Write code that accepts a value of kelvin, converts it to values on the three other scales and prints the result. For instance:

K  21.00

C  -252.15

F  -421.87

R  37.80

D

<lang d>double kelvinToCelsius(in double k) pure nothrow @safe {

   return k - 273.15;

}

double kelvinToFahrenheit(in double k) pure nothrow @safe {

   return k * 1.8 - 459.67;

}

double kelvinToRankine(in double k) pure nothrow @safe {

   return k * 1.8;

}

unittest {

   import std.math: approxEqual;
   assert(approxEqual(kelvinToCelsius(21.0), -252.15));
   assert(approxEqual(kelvinToFahrenheit(21.0), -421.87));
   assert(approxEqual(kelvinToRankine(21.0), 37.8));

}

void main(string[] args) {

   import std.stdio, std.conv, std.string;

   if (args.length == 2 && isNumeric(args[1])) {
       immutable kelvin = to!double(args[1]);
       if (kelvin >= 0) {
           writefln("K  %2.2f", kelvin);
           writefln("C  %2.2f", kelvinToCelsius(kelvin));
           writefln("F  %2.2f", kelvinToFahrenheit(kelvin));
           writefln("R  %2.2f", kelvinToRankine(kelvin));
       } else
           writefln("%2.2f K is below absolute zero", kelvin);
   }

}</lang>

Output:

K  21.00

C  -252.15

F  -421.87

R  37.80

J

Solution:<lang j> NB. Temp conversions are all linear polynomials

  K2K    =:     0    1    NB. K = (1  *k) +   0
  K2C    =:  _273    1    NB. C = (1  *k) - 273
  K2F    =:  _459.67 1.8  NB. F = (1.8*k) - 459.67
  K2R    =:     0    1.8  NB. R = (1.8*k) +   0

  NB.  Do all conversions at once (eval 
  NB.  polynomials in parallel). This is the
  NB.  numeric matrix J programs would manipulate
  NB.  directly.
  k2KCFR =:  (K2K , K2C , K2F ,: K2R) p./ ]</lang>

Example:<lang j> NB. Format matrix for printing

  fmt    =:  '0.2' 8!:0 k2KCFR

  NB.  Tag each temp with scale, for human
  NB.  legibility.
  kcfr   =:  0 _1 |: 'KCFR' ,"0 1"_1 >@:fmt
  
  kcfr 21

K 21.00 C-252.00 F-421.87 R 37.80

  kcfr 0 NB. Absolute zero

K 0.00 C-273.00 F-459.67 R 0.00

  kcfr 21 100 300  NB. List of temps works fine

K 21.00 C-252.00 F-421.87 R 37.80

K 100.00 C-173.00 F-279.67 R 180.00

K 300.00 C 27.00 F 80.33 R 540.00

  </lang>

Notes: The approach is founded on polynomials, one for each conversion (e.g. Fahrenheit = 1.8*x - 459.67 where x is measured in degrees Kelvin), and all polynomials are evaluated simultaneously using the built-in p.. Through some code decorations (specifically the / in p./ the "0 1"_1 and the 0 _1 |:), we permit our function to convert arrays of temperatures of arbitrarily high dimension (a single temp, lists of temps, tables of temps, cubes of temps, etc).

Python

<lang python>>>> while True: k = float(input('K ? ')) print("%g Kelvin = %g Celsius = %g Fahrenheit = %g Rankine degrees." % (k, k - 273.15, k * 1.8 - 459.67, k * 1.8))

K ? 21.0 21 Kelvin = -252.15 Celsius = -421.87 Fahrenheit = 37.8 Rankine degrees. K ? 222.2 222.2 Kelvin = -50.95 Celsius = -59.71 Fahrenheit = 399.96 Rankine degrees. K ? Traceback (most recent call last):

 File "<pyshell#4>", line 2, in <module>
   k = float(input('K ? '))

KeyboardInterrupt >>> </lang>

Python: Universal conversion

This converts from any one of the units to all the others <lang python>>>> toK = {'C': (lambda c: c + 273.15),

          'F': (lambda f: (f + 459.67) / 1.8),
          'R': (lambda r: r / 1.8),
          'K': (lambda k: k) }

>>> while True: magnitude, unit = input('<value> <K/R/F/C> ? ').split() k = toK[unit](float(magnitude)) print("%g Kelvin = %g Celsius = %g Fahrenheit = %g Rankine degrees." % (k, k - 273.15, k * 1.8 - 459.67, k * 1.8))

<value> <K/R/F/C> ? 222.2 K 222.2 Kelvin = -50.95 Celsius = -59.71 Fahrenheit = 399.96 Rankine degrees. <value> <K/R/F/C> ? -50.95 C 222.2 Kelvin = -50.95 Celsius = -59.71 Fahrenheit = 399.96 Rankine degrees. <value> <K/R/F/C> ? -59.71 F 222.2 Kelvin = -50.95 Celsius = -59.71 Fahrenheit = 399.96 Rankine degrees. <value> <K/R/F/C> ? 399.96 R 222.2 Kelvin = -50.95 Celsius = -59.71 Fahrenheit = 399.96 Rankine degrees. <value> <K/R/F/C> ? </lang>