From 820672ec0be0bc60a984cc21564bcdaf349bbdfe Mon Sep 17 00:00:00 2001
From: Michele Peresano <peresano@mpp.mpg.de>
Date: Mon, 20 Jan 2025 15:39:13 +0100
Subject: [PATCH 1/3] Allow LogParabola to be define using natural log

---
 pyirf/spectral.py | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/pyirf/spectral.py b/pyirf/spectral.py
index 182657bf..4e4d4533 100644
--- a/pyirf/spectral.py
+++ b/pyirf/spectral.py
@@ -195,25 +195,32 @@ class LogParabola:
         :math:`\beta`
     e_ref: astropy.units.Quantity[energy]
         :math:`E_\text{ref}`
+    from_log10: bool
+        If True, compute the energy ration in the exponent factor
+        using base 10, else use natural logarithm.
     """
 
     @u.quantity_input(
         normalization=[DIFFUSE_FLUX_UNIT, POINT_SOURCE_FLUX_UNIT], e_ref=u.TeV
     )
-    def __init__(self, normalization, a, b, e_ref=1 * u.TeV):
+    def __init__(self, normalization, a, b, e_ref=1 * u.TeV, from_log10=True):
         """Create a new LogParabola spectrum"""
         self.normalization = normalization
         self.a = a
         self.b = b
         self.e_ref = e_ref
+        self.from_log10 = from_log10
 
     @u.quantity_input(energy=u.TeV)
     def __call__(self, energy):
         e = (energy / self.e_ref).to_value(u.one)
-        return self.normalization * e ** (self.a + self.b * np.log10(e))
+        log_factor = np.log10(e) if self.from_log10 else np.log(e)
+        return self.normalization * e ** (self.a + self.b * log_factor)
 
     def __repr__(self):
-        return f"{self.__class__.__name__}({self.normalization} * (E / {self.e_ref})**({self.a} + {self.b} * log10(E / {self.e_ref}))"
+        log_factor = "log10" if self.from_log10 else "ln"
+        str_rep = f"{self.__class__.__name__}({self.normalization} * (E / {self.e_ref})**({self.a} + {self.b} * {log_factor}(E / {self.e_ref}))"
+        return str_rep
 
 
 class PowerLawWithExponentialGaussian(PowerLaw):

From a1029eba73ea05a4a5353dff627dc888226617b4 Mon Sep 17 00:00:00 2001
From: Michele Peresano <peresano@mpp.mpg.de>
Date: Mon, 20 Jan 2025 16:07:50 +0100
Subject: [PATCH 2/3] Add unit test for spectral.LogParabola

---
 pyirf/tests/test_spectral.py | 57 ++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/pyirf/tests/test_spectral.py b/pyirf/tests/test_spectral.py
index fcf68712..1c5742ba 100644
--- a/pyirf/tests/test_spectral.py
+++ b/pyirf/tests/test_spectral.py
@@ -74,6 +74,63 @@ def test_powerlaw():
     assert power_law(1 * u.TeV).unit == unit
     assert power_law(1 * u.GeV).unit == unit
 
+def test_logparabola():
+    from pyirf.spectral import LogParabola
+
+    # Test initialization
+    normalization = 1e-12 * u.Unit("cm-2 s-1 TeV-1")
+    a = -2.0
+    b = 0.1
+    e_ref = 1 * u.TeV
+    lp = LogParabola(normalization, a, b, e_ref, from_log10=True)
+
+    assert lp.normalization == normalization
+    assert lp.a == a
+    assert lp.b == b
+    assert lp.e_ref == e_ref
+    assert lp.from_log10 is True
+
+    # Test the flux evaluation at a given energy
+    normalization = 1e-12 * u.Unit("cm-2 s-1 TeV-1")
+    a = -2.0
+    b = 0.1
+    e_ref = 1 * u.TeV
+    lp = LogParabola(normalization, a, b, e_ref, from_log10=True)
+
+    energy = 2 * u.TeV
+    expected_flux = normalization * (energy / e_ref) ** (
+        a + b * np.log10(energy / e_ref)
+    )
+    calculated_flux = lp(energy)
+
+    assert u.isclose(
+        calculated_flux, expected_flux, atol=1e-20 * u.Unit("cm-2 s-1 TeV-1")
+    )
+
+    # Same but for natural log
+    normalization = 1e-12 * u.Unit("cm-2 s-1 TeV-1")
+    a = -2.0
+    b = 0.1
+    e_ref = 1 * u.TeV
+    lp = LogParabola(normalization, a, b, e_ref, from_log10=False)
+
+    energy = 2 * u.TeV
+    expected_flux = normalization * (energy / e_ref) ** (a + b * np.log(energy / e_ref))
+    calculated_flux = lp(energy)
+
+    assert u.isclose(
+        calculated_flux, expected_flux, atol=1e-20 * u.Unit("cm-2 s-1 TeV-1")
+    )
+
+    # Test string representation
+    normalization = 1e-12 * u.Unit("cm-2 s-1 TeV-1")
+    a = -2.0
+    b = 0.1
+    e_ref = 1 * u.TeV
+    lp = LogParabola(normalization, a, b, e_ref, from_log10=True)
+
+    expected_repr = "LogParabola(1e-12 1 / (TeV s cm2) * (E / 1.0 TeV)**(-2.0 + 0.1 * log10(E / 1.0 TeV))"
+    assert repr(lp) == expected_repr
 
 def test_powerlaw_from_simulations():
     from pyirf.simulations import SimulatedEventsInfo

From bffea3dab959989cd0efc151f9cd9dff743dbdd2 Mon Sep 17 00:00:00 2001
From: Michele Peresano <peresano@mpp.mpg.de>
Date: Mon, 20 Jan 2025 16:08:41 +0100
Subject: [PATCH 3/3] Add news fragment for PR #295

---
 docs/changes/295.api.rst | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 docs/changes/295.api.rst

diff --git a/docs/changes/295.api.rst b/docs/changes/295.api.rst
new file mode 100644
index 00000000..41746f8b
--- /dev/null
+++ b/docs/changes/295.api.rst
@@ -0,0 +1 @@
+Allow a LogParabola spectral model to be initialized with a logarithm in base 10 or a natural logarithm using the boolean attribute `from_log10`.
\ No newline at end of file