Example 4: Get abundance from REW
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About
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This example will show you how to derive the lithium abundance given a REW by using the ``Rew`` class in ``breidablik.interpolate.rew``.

Example
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Lets assume we want to find the 3D NLTE abundance for a REW of -6 for LP 815-43.

::

  REW = -6
  # stellar parameters for LP 815-43
  t_eff = 6400 # K
  log_g = 4.17 # cgs
  met = -2.74 # dex

Next, we load in the models by initialising the class, then call the function ``find_abund`` with the parameters we just defined.

::

  from breidablik.interpolate.rew import Rew
  # initialise model
  model = Rew()
  # find abundance
  abund = model.find_abund(t_eff, log_g, met, REW)
  print(abund)

Which returns an abundance of 1.70 dex.

``find_abund`` accepts a parameter: ``center``, that determines which model is used: there are 3 models, 1 for each Li line. The 3 lithium lines are centered at 610.5298, 670.9659, and 812.8606 nm. The input ``center`` value will snap to the closest value out of those 3. By default, the 670.9 nm model is used.

The 3D stagger grid does not go to low temperatures. For M-type stars, we can calculate 1D NLTE A(Li) trained on the marcs grid.

::

  # initialise model trained on 1D NLTE A(Li)
  model = Rew(dim = 1)

This 1D model was only trained on the 670.9 nm line. If you call ``find_abund`` using a different Li line, a warning will be raised and ``find_abund`` will return a 3D NLTE abundance for the specified line.