# Calculate a full range spectrum¶

We compute the transmittance of an homogeneous, 1-km atmosphere layer at 300 K and 1 atm, with 420 ppm CO2 and 2% H2O.

This example makes use of a lot of the RADIS optimization and convenience functions :

• The database is retrieved from the latest HITRAN data using [HAPI], parsed with RADIS and stored to memory-mapping formats. After the first calls, retrieving the database will be very fast

• The RADIS algorithm includes a sparse wavenumber implementation, which is activated by default in the following example where the waverange is very large. This behavior can be changed by setting the `SPARSE_WAVENUMBER` key of the `radis.config` dictionary, or of the ~/radis.json user file.

• The wavenumber grid is automatically computed using the `wstep='auto'` parameter.

• A linestrength cutoff reduces the initial number of lines.

Eventually, the full-range spectrum (about 4.8M points) is computed within a minute, with about 140k lines resolved, i.e. a performance of about 1e10 gridpoints*lines/s.

Extra optimization could be achieved by cutting the spectrum in small intervals, but requires an a-priori knowledge of the absorption & emission ranges of the spectrum. See the Calculate a large spectrum by part

```import astropy.units as u

from radis import calc_spectrum

s = calc_spectrum(
wmin=0.5 * u.um,
wmax=15 * u.um,  # cm-1
mole_fraction={"CO2": 420e-6, "H2O": 0.02},
isotope="1,2,3",
pressure=1.01325,  # bar
Tgas=300,  # K
path_length=1e5,  # 1 km in cm
verbose=2,
databank="hitran",
wstep="auto",
)
```

Plot low and high resolution spectra on the same graph :

```s.apply_slit(10, "nm")
import matplotlib.pyplot as plt

plt.figure(figsize=(16, 6))
s.plot("transmittance_noslit", wunit="nm", color="k", alpha=0.1, nfig="same")
s.plot("transmittance", wunit="nm", color="k", nfig="same")
```

Print some details about the computed spectrum : We could also simply use `print(s)`

```print("Number of grid points: ", len(s))
print(
"Number of lines: ", s.c["total_lines"]
)  # some are discarded by linestrength cutoff
print("Number of lines: ", s.c["lines_calculated"])
print("Whether the sparse wavenumber algorithm was activated: ", s.c["sparse_ldm"])
print(f"Lineshape truncation used: {s.c['truncation']:.1f}cm-1")
print(f"Total calculation time: {s.c['calculation_time']:.1f}s")
print(
f"Gridpoints * lines/s : {len(s)*s.c['lines_calculated']/s.c['calculation_time']:.1e}"
)
```

Total running time of the script: ( 0 minutes 0.000 seconds)