What is the best way to insure that all of my functions are using the same constant values?
11 visualizaciones (últimos 30 días)
Mostrar comentarios más antiguos
Jim Riggs
el 17 de Sept. de 2019
Comentada: Jim Riggs
el 15 de Nov. de 2022
I want to make sure that my functions are all using the same values for physical constants, like earth radius, elipsoidal flattening, etc. and avoid hard-coding a bunch of constant values in each function.
Some people advocate using a function that returns constant values, e.g.
Re = LibraryConstant('Earth_Radius');
f = LibraryConstant('Ellipsoid_flattening');
ev = LibraryConstant('electron_volt');
...
The function "LibraryConstant" is a big case-select structure that returns the requested value.
Or, you might define a bunch of global constants, but this seems like an undesirable approach.
What about creating a structure or table that contains all of the constants - this would have to be passed as an additinal argumernt to each function.
What would you recommend as an efficient method?
Respuesta aceptada
Steven Lord
el 17 de Sept. de 2019
classdef myconstants
properties(Constant)
g = 9.8;
g_units = 'm/s/s';
c = 299792458;
c_units = 'm/s';
end
end
This is similar to James Tursa's struct based approach, but with one major difference: you don't need to call a function to create the struct in your workspace. You just reference the property with the name.
>> x = myconstants.c
x =
299792458
You can even give your properties help text. [This is documented in the documentation for the help function.]
classdef myconstants
properties(Constant)
% g is the gravity of Earth
% (https://en.wikipedia.org/wiki/Gravity_of_Earth)
g = 9.8;
g_units = 'm/s/s';
% c is the speed of light in a vacuum
c = 299792458;
c_units = 'm/s';
end
end
>> help myconstants.g
6 comentarios
Más respuestas (1)
James Tursa
el 17 de Sept. de 2019
I use a function that returns a structure, containing the values and the unit descriptions. Your code can either pass this structure around, or call the function. E.g.,
function e = earth
e.re = 6378.137; % equatorial radius
e.re_units = 'km';
e.we = 7.2921150e-5; % rotation rate
e.we_units = 'radians/sec';
e.flatinv = 298.257223563;
:
end
I put the units as strings so that simply displaying the structure will show me what the units are.
2 comentarios
Orion Smedley
el 15 de Nov. de 2022
Would this run through the entire earth function every time you calll say earth.re? Or would it just run until it got to earth.re and then quit?
(not an issue if the constants are just numbers like this, but this may be an issue if the constants have to be numerically calculated.)
Ver también
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!