Parameters

We have already seen at least how to:

• request a parameter when constructing an experiment (ns.reqparameter(...));

• find a parameter and change its value (ns[...].set(v) or ns --value ... v ).

Here we’ll try some more examples. First, let’s try to make the gaussianpeak model reuse existing Mu parameter, that will be in separate namespace which we’ll call common:

python ./gna -- ns --define common.Mu central=1 sigma=0.01 \
                --push common
             -- gaussianpeak --name peak1

With the first command (ns) we have defined new parameter with full path common.Mu, central value 1 and absolute uncertainty 0.1 and then activated the common namespace by using the --push option. Activation means that each name inside the common namespace will be available during lookups, in particular during object binding. Since Mu parameter will be available during gaussianpeak execution, the corresponding ns.reqparameter won’t create any new parameter. In other words, there will be no peak1.Mu as before and common.Mu will be used by our observable instead. As a consequence, as we have already set its central (and default) value to 1, if you’ll plot the peak1.spectrum, you’ll see the peak without any additional ns --value.

In the same manner, we can create several experimental models and make some parameters shared between them. For example, if we have two different experiments, that are expecting to observe two different and independent peaks, but with exactly the same background rate, it makes sense to make the BackgroundRate parameter common:

python ./gna -- ns --define common.BackgroundRate central=1 sigma=0.1 \
                --push common
             -- gaussianpeak --name peak1
             -- gaussianpeak --name peak2
             -- ns --value peak1.Mu 1 --value peak2.Mu 2
             -- spectrum --plot peak1/spectrum --plot peak2/spectrum
             -- ns --value common.BackgroundRate 2
             -- spectrum --plot peak1/spectrum --plot peak2/spectrum

As you can see, we treat Mu of both peaks independently, while the background rate is really common and affects both peaks at the same time.

As an example do it vice-versa.