Create Ultra pset energy bins (#811)

* pset energy bins

imap_processing/tests/ultra/unit/test_ultra_l1c_pset_bins.py

@@ -0,0 +1,19 @@
+"Tests bins for pointing sets"
+
+import numpy as np
+
+from imap_processing.ultra.l1c.ultra_l1c_pset_bins import build_energy_bins
+
+
+def test_build_energy_bins():
+    """Tests build_energy_bins function."""
+    energy_bin_start, energy_bin_end = build_energy_bins()
+
+    assert energy_bin_start[0] == 3.5
+    assert len(energy_bin_start) == 90
+    assert len(energy_bin_end) == 90
+
+    # Comparison to expected values
+    np.testing.assert_allclose(energy_bin_end[0], 3.6795, atol=1e-4)
+    np.testing.assert_allclose(energy_bin_start[-1], 299.9724, atol=1e-4)
+    np.testing.assert_allclose(energy_bin_end[-1], 315.3556, atol=1e-4)

imap_processing/ultra/l1c/ultra_l1c_pset_bins.py

@@ -0,0 +1,29 @@
+"""Module to create energy bins for pointing sets."""
+
+import numpy as np
+
+
+def build_energy_bins() -> tuple[np.ndarray, np.ndarray]:
+    """
+    Build energy bin boundaries.
+
+    Returns
+    -------
+    energy_bin_start : np.ndarray
+        Array of energy bin start values.
+    energy_bin_end : np.ndarray
+        Array of energy bin end values.
+    """
+    alpha = 0.05  # deltaE/E
+    energy_start = 3.5  # energy start for the Ultra grids
+    n_bins = 90  # number of energy bins
+
+    # Calculate energy step
+    energy_step = (1 + alpha / 2) / (1 - alpha / 2)
+
+    # Create energy bins.
+    bin_edges = energy_start * energy_step ** np.arange(n_bins + 1)
+    energy_bin_start = bin_edges[:-1]
+    energy_bin_end = bin_edges[1:]
+
+    return energy_bin_start, energy_bin_end