Disperse

class baseband.tasks.Disperse(ih, dm, *, reference_frequency=None, samples_per_frame=None, frequency=None, sideband=None)

Bases: PaddedTaskBase

Coherently disperse a time stream.

Parameters:

ihtask or baseband stream reader

Input data stream, with time as the first axis.

dmfloat or DispersionMeasure quantity

Dispersion measure. If negative, will dedisperse correctly, but clearer to use the Dedisperse class.

reference_frequencyQuantity, optional

Frequency to which the data should be dispersed. Can be an array. By default, the mean frequency.

samples_per_frameint, optional

Number of dispersed samples which should be produced in one go. The number of input samples used will be larger to avoid wrapping. If not given, the minimum length that gives at least 75% efficiency and ensures efficient fast fourier transforms.

frequencyQuantity, optional

Frequencies for each channel in ih (channelized frequencies will be calculated). Default: taken from ih (if available).

sidebandarray, optional

Whether frequencies in ih are upper (+1) or lower (-1) sideband. Default: taken from ih (if available).

See also

baseband_tasks.fourier.fft_maker

to select the FFT package used.

baseband_tasks.dispersion.Dedisperse

for coherent dedispersion

baseband_tasks.dispersion.DisperseSamples

for incoherent dispersion

Attributes Summary

closed
complex_data
dm
dtype	Data type of the output.
meta
ndim	Number of dimensions of the output.
offset
phase_factor	Phase offsets of the Fourier-transformed frame.
sample_rate	Number of complete samples per second.
sample_shape	Shape of a complete sample.
samples_per_frame	Number of samples per frame of data.
shape	Shape of the output.
size	Number of component samples in the output.
start_time	Start time of the output.
stop_time	Time at the end of the output, just after the last sample.
time	Time of the sample pointer's current offset in the output.

Methods Summary

close()	Close task.
read([count, out])	Read a number of complete samples.
seek(offset[, whence])	Change the sample pointer position.
task(data)
tell([unit])	Current offset in the file.

Attributes Documentation

closed = False

complex_data

dm

dtype

Data type of the output.

meta = None

ndim

Number of dimensions of the output.

offset = 0

phase_factor

Phase offsets of the Fourier-transformed frame.

sample_rate

Number of complete samples per second.

sample_shape

Shape of a complete sample.

samples_per_frame

Number of samples per frame of data.

For compatibility with file readers, to help indicate what a nominal chunk of data is.

shape

Shape of the output.

size

Number of component samples in the output.

start_time

Start time of the output.

See also time and stop_time.

stop_time

Time at the end of the output, just after the last sample.

See also start_time and time.

time

Time of the sample pointer’s current offset in the output.

See also start_time and stop_time.

Methods Documentation

close()

Close task.

Note that this does not explicitly close the underlying source; instead, it just deletes the reference to it.

read(count=None, out=None)

Read a number of complete samples.

Parameters:

countint or None, optional

Number of complete samples to read. If None (default) or negative, the number of samples left. Ignored if out is given.

outNone or array, optional

Array to store the samples in. If given, count will be inferred from the first dimension; the remaining dimensions should equal sample_shape.

Returns:

outndarray of float or complex

The first dimension is sample-time, and the remaining ones are as given by sample_shape.

seek(offset, whence=0)

Change the sample pointer position.

This works like a normal filehandle seek, but the offset is in samples (or a relative or absolute time).

Parameters:

offsetint, Quantity, or Time

Offset to move to. Can be an (integer) number of samples, an offset in time units, or an absolute time. For the latter two, the pointer will be moved to the nearest integer sample.

whence{0, 1, 2, ‘start’, ‘current’, or ‘end’}, optional

Like regular seek, the offset is taken to be from the start if whence=0 (default), from the current position if 1, and from the end if 2. One can alternativey use ‘start’, ‘current’, or ‘end’ for 0, 1, or 2, respectively. Ignored if offset is a time.

task(data)

tell(unit=None)

Current offset in the file.

Parameters:

unitUnit or str, optional

Time unit the offset should be returned in. By default, no unit is used, i.e., an integer enumerating samples is returned. For the special string ‘time’, the absolute time is calculated.

Returns:

offsetint, Quantity, or Time

Offset in current file (or time at current position).