Module functions to retrieve photon-space energy grids over which models are evaluated.
{Struct_Type | Array_Type} get_photon_energy_axes([Integer_Type])
{Struct_Type | Array_Type} get_photon_energy_baxes([Integer_Type])
{Struct_Type | Array_Type} get_full_photon_energy_axes([Integer_Type])
{Struct_Type | Array_Type} get_full_photon_energy_baxes([Integer_Type])
Error Return Value: NULL
Arguments:
(1) data set number (default 1)
In Sherpa parlance, a ``dataspace'' is an
N-dimensional
grid defined by the independent variables of the dataset
(i.e., x_i in the expression
y = f(x_0, x_1,...,x_(N-1))).
Simple examples include the CHANNELS array in PHA
datasets and the pixel numbers along each axis of FITS images.
The get_photon_energy_axes() function retrieves the dataspace, or
filtered data set axes of the appropriate data set (if no argument
is given, the axes for data set 1 are retrieved). Regardless of the
current Sherpa ANALYSIS setting, this function
returns the dataspace in units of energy (keV). However,
the dataspace is also translated into ``photon space''. The
get_energy_axes() function returns
the dataspace in ``energy space''. In essence, ``photon space''
is what one would see if one could undo the redistribution of
energies by the detector. (One can't really ``deconvolve'' the
data in this manner with any confidence, but for the purposes
of visualization only, the data from the appropriate
RMF and ARF files are used to estimate what the data would look
like after a ``deconvolution''.)
Thus, for example, if one is
working with filtered PHA data in energy-space, what is returned are the
low and high bin boundaries in keV (quantities assigned,
e.g., by the ENERG_LO and ENERG_HI
columns of the ARF). But if one is working in wavelength-space
or channel-space, the bin boundaries returned are still in keV.
These boundaries generally do not match the boundaries
that would be returned by get_energy_[b]axes().
(The function get_photon_energy_baxes() acts as
get_photon_energy_axes(), save that it retrieves the dataspace
for the background associated with the appropriate data set.)
One may display photon-space model amplitudes et al. on the same grid output by
get_photon_axes using the
Sherpa plotting commands
LPLOT SOURCE et al.
Read the PHA file with the ARF/RMF defined in the header (qso.pha).
Define the model, filter the data and fit.
sherpa> data qso.pha
sherpa> foo0=get_photon_energy_axes()
sherpa> print(foo0)
NULL
sherpa> source = xsphabs[abs]*pow[p1]
abs.nH parameter value [0.1]
p1.gamma parameter value [1]
p1.ref parameter value [1]
p1.ampl parameter value [0.00059008]
sherpa>
sherpa> ignore energy :0.2,10:
sherpa> fit
LVMQT: V2.0
LVMQT: initial statistic value = 297162
LVMQT: final statistic value = 275.333 at iteration 7
abs.nH 0.0245136 10**22 atoms/cm**2
p1.gamma 1.53707
p1.ampl 5.91298e-05
Obtain the photon energy axes information into "fooO" and print content of
"foo0". Print the value of the 11th low energy in "foo0".
The mid is NULL, so the final print command gives an error information.
sherpa> foo0=get_photon_energy_axes()
sherpa> print(foo0)
axistype = Energy
axisunits = keV
lo = Float_Type[1077]
hi = Float_Type[1077]
mid = NULL
sherpa> print(foo0.lo[10])
0.33
sherpa> print(foo0.mid[10])
Type Mismatch: Context requires an array. Scalar not converted
Type Mismatch: print(foo0.mid[10]);
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guide
- sherpa
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get_analysis,
get_arf_axes,
get_axes,
get_coord,
get_data,
get_energy_axes,
get_errors,
get_filter,
get_filter_expr,
get_fit,
get_fluxed_spectrum,
get_ftest,
get_metadata,
get_photon_axes,
get_photon_wave_axes,
get_qvalue,
get_raw_axes,
get_record,
get_source,
get_statistic,
get_stats,
get_syserrors,
get_wave_axes,
get_weights,
record,
save,
write
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