Enabling spectrum plotting in the frequency domain (#1695)

* allowing frequency plotting

* docstring beginning

* docstring

* Get rid of accidental change

* fixing latex in axis labels

* trying to get axis labels formatted

* fixing axis label

* Fixing small mistake

tardis/montecarlo/spectrum.py

@@ -37,16 +37,19 @@ def __init__(self, _frequency, luminosity):
         self._frequency = _frequency.to("Hz", u.spectral())
         self.luminosity = luminosity.to("erg / s")
 
+        l_nu_unit = u.def_unit('erg\ s^{-1}\ Hz^{-1}', u.Unit('erg/(s Hz)'))
+        l_lambda_unit = u.def_unit('erg\ s^{-1}\ \\AA^{-1}', u.Unit('erg/(s AA)'))
+
         self.frequency = self._frequency[:-1]
         self.delta_frequency = self._frequency[1] - self._frequency[0]
         self.wavelength = self.frequency.to("angstrom", u.spectral())
 
         self.luminosity_density_nu = (
             self.luminosity / self.delta_frequency
-        ).to("erg / (s Hz)")
+        ).to(l_nu_unit)
         self.luminosity_density_lambda = self.f_nu_to_f_lambda(
             self.luminosity_density_nu,
-        )
+        ).to(l_lambda_unit)
 
     @property
     def flux_nu(self):
@@ -100,19 +103,34 @@ def f_nu_to_f_lambda(self, f_nu):
         return f_nu * self.frequency / self.wavelength
 
     def plot(self, ax=None, mode="wavelength", **kwargs):
+        """plots the TARDISSpectrum
+
+        Parameters
+        ----------
+        ax : matplotlib.axes.Axes, optional
+            axes to plot on, by default None
+        mode : str, optional
+            plot against wavelength or frequency, by default "wavelength"
+        """        
         if ax is None:
             from matplotlib.pyplot import gca
 
             ax = gca()
         if mode == "wavelength":
-            ax.plot(
-                self.wavelength.value,
-                self.luminosity_density_lambda.value,
-                **kwargs,
+            ax.plot(self.wavelength.value, self.luminosity_density_lambda.value, **kwargs)
+            ax.set_xlabel(
+                f"Wavelength [{self.wavelength.unit.to_string('latex_inline')}]"
+            )
+            ax.set_ylabel(
+                f"$L_\\lambda$ [{self.luminosity_density_lambda.unit.to_string('latex_inline')}]"
+            )
+        elif mode == "frequency":
+            ax.plot(self.frequency.value, self.luminosity_density_nu.value, **kwargs)
+            ax.set_xlabel(
+                f"Frequency [{self.frequency.unit.to_string('latex_inline')}]"
             )
-            ax.set_xlabel(f"Wavelength [{self.wavelength.unit._repr_latex_()}]")
             ax.set_ylabel(
-                f"Flux [{self.luminosity_density_lambda.unit._repr_latex_():s}]"
+                f"$L_\\nu$ [{self.luminosity_density_nu.unit.to_string('latex_inline')}]"
             )
         else:
             warnings.warn(f"Did not find plotting mode {mode}, doing nothing.")