Units
Table of contents
Units in REST
The units inside REST-for-Physics are available in the namespace REST_Units, a namespace defines a set of variables and methods that are accessible under that name when invoking REST_Units::.
Inside a restRoot session we can use the namespace to identify which public data members and methods are available to us. Now, just open a new restRoot session and checkout what it is inside the namespace.
restRoot
root [0] REST_Units:: [TAB]
In particular, you will be able to identify few of the REST basic units defined inside.
You may check now the scaling value associated to each unit.
root [0] REST_Units::degrees [ENTER]
(const double) 57.295780
Where the returned value corresponds to the degrees in one radian. The units inside REST work in a way that we can access the scaling factor by invoking units("UNIT_STRING"), which will allow us to make unit conversions inside our code.
For example, if we execute,
root [1] 1. * units("cm")
(double) 0.10000000
the result will be the number of cm inside 1 mm which is the default unit inside REST. We can also combine different units to achieve more complex results, such as:
root [2] 1. * units("g/cm^3")
(double) 1000000.0
If we know the value the units for the value we are providing, and this is not given in the default units, we will then need to write a more generic expression:
root [3] 180. * units("rads")/units("degrees")
(double) 3.1415927
REMEMBER: All these lines of code that you are using inside your restRoot session can be used inside a C++ compiled code, a C-macro, or even a python script that imports the REST-for-Physics libraries.
TRestPhysics
In the same way as units, REST-for-Physics provides access to its own physics constant definitions and geometry methods commonly exploited in particle tracking.
Check inside the REST_Physics namespace to see the available constants and print out their value.
root [4] REST_Physics:: [TAB]
root [5] REST_Physics::lightSpeed
(const double) 2.9979246e+08
Additional Resources
- See day2/session1 of the [rest-school github repository]{https://github.com/rest-for-physics/rest-school/tree/master/day2/session1} to access the codes.