Re: standard units in software

[Eugene Chudakov <gen@jlab.org>]

Hi Matt,

how do you treat stored parameters, say the particles' masses?
Do you have also default units in the header in order to treat
the stored variables, something unspecified like "m_unit", 
additionally to "m_GeV"?

Thanks,
Eugene

On Mon, 24 Nov 2008, Matthew Shepherd wrote:

>
> Sorry, there's an (obvious) typo here:
>
> Should be:
>
> bool checkEnergy( double energy ){
>
> return( energy > 30*k_MeV );
> }
>
> Eugene is right -- more CPU cycles and typing.  But I think readability and 
> odds of making a mistake and introducing a bug are greatly reduced.
>
> -Matt
>
> On Nov 24, 2008, at 2:39 PM, Matthew Shepherd wrote:
>
>> 
>> Hi Eugene,
>> 
>> Other routines can use the same global constants.  For example:
>> 
>> suppose showerEnergy is some energy expressed internally in an object in 
>> standard units.  Then:
>> 
>> if( checkEnergy( showerEnergy ) ){
>> ...
>> }
>> 
>> bool checkEnergy( double energy ){
>> 
>> return( energy*k_MeV > 30*k_MeV );
>> }
>> 
>> One just needs to be sure:
>> 
>> #include "units.h"
>> 
>> exists wherever the global constants need to be used.
>> 
>> In other words, the numbers are always expressed in standard units.  Having 
>> the constants just helps alleviate keeping track of what the units are.  If 
>> the standard units are MeV then k_MeV == 1, k_GeV == 0.001, etc..
>> 
>> -Matt
>> 
>