Unit management

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Detailed Description

The unit manager converts values from one unit to another.

The unit manager reads the file unitfile.txt. The file loaded is the first found according the following search sequence:

• The current directory
• The same directory as the executable gridlabd.exe
• The path in the GLPATH environment variable.

Units are based on 6 physical/economic constants:

	#c=2.997925e8 ; speed of light (m/s)
	#e=1.602189246e-19 ; electron charge (C)
	#h=6.62617636e-24 ; Plank's constant (kg.m.m/s)
	#k=1.38066244e-13 ; Boltzman's constant (kg.m.m/s.s.K)
	#m=9.10953447e-31 ; electron rest mass (kg)
	#s=1.233270e4 ; average price of gold in 1990 ($/kg - 383.59$/oz)
	

From these are derived all the fundamental SI units:

	m=-1,0,1,0,-1,0,4.121487e01,0,7
	kg=0,0,0,0,1,0,1.09775094e30,0,10
	s=-2,0,1,0,-1,0,1.235591e10,0,7
	A=2,1,-1,0,1,0,5.051397e08,0,7
	K=2,0,0,-1,1,0,1.686358e00,0,7
	cd=4,0,-1,0,2,0,1.447328E+00,0,7
	

An addition currency unit is defined because it's really useful:

	1990$=0,0,0,0,1,1,1.097751e30,0,7
	

Based on these units, all the other units are derived using simple formulae, e.g.:

	; Length
	cm=0.01 m
	mm=0.001 m
	km=1000 m
	in=2.54 cm
	ft=12 in
	yd=3 ft
	mile=5280 ft
	

of Operation

The theory behind the unit management system is based on the fact that every physical quantity can be expressed in terms of a linear combination of exponents of the five basic physical constants (to which a currency constant is added to allow cost-based units). This is best understood by considering the equation

where

where c, e, h, k, m, and s are the constants defined above, and the k terms are the unit terms defined for that unit.

Thus, two values can only be added (or subtracted) only if their units are the same (i.e., unit is a common factor), and when two values are multiplied (or divided), the exponential terms of the units are added (or subtracted).

For example, 1 second is defined as

Typedefs
typedef struct s_unit	UNIT
	the UNIT structure
Functions
int	unit_convert (char *from, char *to, double *pValue)
	Convert a value from one unit to another.
int	unit_convert_complex (UNIT *pFrom, UNIT *pTo, complex *pValue)
	Convert a complex value from one unit to another.
int	unit_convert_ex (UNIT *pFrom, UNIT *pTo, double *pValue)
	Convert a value from one unit to another.
UNIT *	unit_find (char *unit)
	Find a unit.
void	unit_init (void)
	Initialize the unit manager.
int	unit_test (void)
	Test the unit manager.

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Function Documentation

int unit_convert	(	char *	from,
		char *	to,
		double *	pValue
	)

Convert a value from one unit to another.

Returns:

1 if successful, 0 if failed

Definition at line 608 of file unit.c.

Referenced by convert_unit_double(), and unit_test().

int unit_convert_complex	(	UNIT *	pFrom,
		UNIT *	pTo,
		complex *	pValue
	)

Convert a complex value from one unit to another.

Returns:

1 if successful, 0 if failed

Definition at line 656 of file unit.c.

References output_error().

int unit_convert_ex	(	UNIT *	pFrom,
		UNIT *	pTo,
		double *	pValue
	)

Convert a value from one unit to another.

Returns:

1 if successful, 0 if failed

Definition at line 632 of file unit.c.

References output_error().

Referenced by aggregate_mkgroup(), convert_from_complex(), and convert_from_double().

UNIT * unit_find

(

char *

unit

)

Find a unit.

Returns:

a pointer to the UNIT structure

Parameters:

unit	the name of the unit

Definition at line 681 of file unit.c.

References output_error(), and unit_init().

Referenced by aggregate_mkgroup(), class_define_map(), global_create(), and object_get_unit().

int unit_test

(

void

)

Test the unit manager.

Returns:

the number of failed tests

Definition at line 712 of file unit.c.

References output_test(), output_verbose(), and unit_convert().

Referenced by cmdarg_load().