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Developer documentation

Developer documentation#

Here we will cover all the steps required to add new functionality to the sigpyproc package. To do this, we will first consider adding a new function to the Filterbank class.

Adding a new function: bandpass()#

Aim: Add a new function called bandpass, which will return the total power as a function of frequency for our observation.

Files to be modified: sigpyproc/base.py, sigpyproc/core/kernels.py.

Step 1: Write the API part#

The first step is to write the user API of the function. As this function will run on data with both time and frequency resolution, it belongs in the Filterbank class.

def bandpass(self, gulp=512, **kwargs):
    bpass_ar = np.zeros(self.header.nchans, dtype=np.float32)
    num_samples = 0
    for nsamps, ii, data in self.read_plan(**plan_kwargs):
        kernel.extract_bpass(data, bpass_ar, self.header.nchans, nsamps)
        num_samples += nsamps
    bpass_ar = bpass_ar / num_samples
    return TimeSeries(bpass_ar, self.header.new_header({"nchans": 1}))

Looking at the important lines, we have: Return an instance of the TimeSeries class. The TimeSeries class takes two arguments, an instance of numpy.ndarray and an instance of Header.

Now we have something similar to a normal numpy.ndarray, which exports several other methods for convenience.

Step 2: Write the core Numba kernel#

We called a kernel function named extract_bpass. This function belongs in the sigpyproc/core/kernels.py file. In kernels.py, our function looks like:

@njit(["void(u1[:], f4[:], i4, i4)", "void(f4[:], f4[:], i4, i4)"], cache=True, parallel=True)
def extract_bpass(inarray, outarray, nchans, nsamps):
    for ichan in prange(nchans):
        for isamp in range(nsamps):
            outarray[ichan] += inarray[nchans * isamp + ichan]

This function receives a block of data and sums that block along the time axis. We use the jit compiler directive parallel to enable OpenMP threading.

Reporting an issue#

Post an issue on the GitHub repository. When you post an issue, please provide the details to reproduce the issue.

Contributing code or documentation#

An excellent place to start is the AstroPy developer docs.

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