Demonstrate the dense basis approach for describing the SFZH

This script demonstrates how to describe a SFZH in the dense basis formalism. It includes the following steps: - Builds and plots a parametric galaxy using a dense basis representation - Creates spectra from this object

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SUMMARY OF PARAMETERISED STAR FORMATION HISTORY
<class 'synthesizer.parametric.sf_hist.DenseBasis'>
db_tuple: (9.0, -3, 2, 0.3, 0.8)
redshift: 0.1
median age: 2960.00 Myr
mean age: 4342.18 Myr
----------

Pure stellar spectra

import matplotlib.pyplot as plt
import numpy as np
from unyt import Msun

from synthesizer.emission_models import IncidentEmission
from synthesizer.grid import Grid
from synthesizer.parametric import SFH, Stars, ZDist
from synthesizer.parametric.galaxy import Galaxy

if __name__ == "__main__":
    # Define the grid
    grid_name = "test_grid"
    grid_dir = "../../tests/test_grid/"
    grid = Grid(grid_name, grid_dir=grid_dir)

    # define the parameters of the star formation and metal enrichment
    # histories
    sfh_p = (9.0, -3, 2, 0.3, 0.8)
    redshift = 0.1
    stellar_mass = 1e8 * Msun

    # define the functional form of the star formation and metal enrichment
    # histories
    sfh = SFH.DenseBasis(db_tuple=sfh_p, redshift=0.1)
    print(sfh)  # print sfh summary

    sfh.plot()

    # Constant metallicity
    metal_dist = ZDist.DeltaConstant(log10metallicity=-2.0)

    # get the 2D star formation and metal enrichment history for the given SPS
    # grid.
    stars = Stars(
        grid.log10age,
        grid.metallicity,
        sf_hist=sfh,
        metal_dist=metal_dist,
        initial_mass=stellar_mass,
    )

    stars.plot_sfzh()

    time = np.linspace(0, 10, 100)
    plt.plot(time, sfh._sfr(10**time))
    plt.show()

    # create a galaxy object
    galaxy = Galaxy(stars)

    # generate pure stellar spectra alone
    model = IncidentEmission(grid)
    galaxy.stars.get_spectra(model)
    print("Pure stellar spectra")
    galaxy.plot_spectra(
        show=True, combined_spectra=False, stellar_spectra=True
    )