Enhancement to the perturbative modelling (#1002)

* Option to skip updating ptc

* test for ptc update

* Pass extrapolation params along

pyccl/nl_pt/power.py

@@ -445,7 +445,7 @@ def get_pt_pk2d(cosmo, tracer1, tracer2=None, ptc=None,
                 nonloc_pk_type='nonlinear',
                 a_arr=None, extrap_order_lok=1, extrap_order_hik=2,
                 return_ia_bb=False, return_ia_ee_and_bb=False,
-                return_ptc=False):
+                return_ptc=False, update_ptc=True):
     """Returns a :class:`~pyccl.pk2d.Pk2D` object containing
     the PT power spectrum for two quantities defined by
     two :class:`~pyccl.nl_pt.tracers.PTTracer` objects.
@@ -503,6 +503,8 @@ def get_pt_pk2d(cosmo, tracer1, tracer2=None, ptc=None,
             initialized when this function is called. If `False` (default)
             the ptc is not output, whether or not it is initialized as
             part of the function call.
+        update_ptc (bool): if `False`, do not recompute the tracer-independent
+            perturbative quantitities in the fastpt object.
 
     Returns:
         :class:`~pyccl.pk2d.Pk2D`: PT power spectrum.
@@ -530,6 +532,7 @@ def get_pt_pk2d(cosmo, tracer1, tracer2=None, ptc=None,
         ptc = PTCalculator(with_dd=with_dd,
                            with_NC=with_NC,
                            with_IA=with_IA)
+        update_ptc = True
     if not isinstance(ptc, PTCalculator):
         raise TypeError("ptc should be of type `PTCalculator`")
 
@@ -558,8 +561,9 @@ def get_pt_pk2d(cosmo, tracer1, tracer2=None, ptc=None,
     ga = growth_factor(cosmo, a_arr)
     ga4 = ga**4
 
-    # update the PTC to have the require Pk components
-    ptc.update_pk(pk_lin_z0)
+    if update_ptc:
+        # update the PTC to have the require Pk components
+        ptc.update_pk(pk_lin_z0)
 
     if nonlin_pk_type == 'nonlinear':
         Pd1d1 = np.array([nonlin_matter_power(cosmo, ptc.ks, a)
@@ -680,11 +684,15 @@ def get_pt_pk2d(cosmo, tracer1, tracer2=None, ptc=None,
         pt_pk_ee = Pk2D(a_arr=a_arr,
                         lk_arr=np.log(ptc.ks),
                         pk_arr=p_pt[0].T,
-                        is_logp=False)
+                        is_logp=False,
+                        extrap_order_lok=extrap_order_lok,
+                        extrap_order_hik=extrap_order_hik)
         pt_pk_bb = Pk2D(a_arr=a_arr,
                         lk_arr=np.log(ptc.ks),
                         pk_arr=p_pt[1].T,
-                        is_logp=False)
+                        is_logp=False,
+                        extrap_order_lok=extrap_order_lok,
+                        extrap_order_hik=extrap_order_hik)
         if return_ptc:
             return pt_pk_ee, pt_pk_bb, ptc
         else:
@@ -693,7 +701,9 @@ def get_pt_pk2d(cosmo, tracer1, tracer2=None, ptc=None,
         pt_pk = Pk2D(a_arr=a_arr,
                      lk_arr=np.log(ptc.ks),
                      pk_arr=p_pt.T,
-                     is_logp=False)
+                     is_logp=False,
+                     extrap_order_lok=extrap_order_lok,
+                     extrap_order_hik=extrap_order_hik)
         if return_ptc:
             return pt_pk, ptc
         else:

pyccl/tests/test_pt_power.py

@@ -333,3 +333,21 @@ def test_return_ptc():
     assert np.allclose(pk_2.eval(ks, 1., COSMO), pk.eval(ks, 1., COSMO))
     assert np.allclose(pee2_2.eval(ks, 1., COSMO), pee2.eval(ks, 1., COSMO))
     assert np.allclose(pbb2_2.eval(ks, 1., COSMO), pbb2.eval(ks, 1., COSMO))
+
+
+def test_pt_no_ptc_update():
+    pee1 = ccl.nl_pt.get_pt_pk2d(COSMO, TRS['TI'], ptc=PTC)
+    pee1_no_update = ccl.nl_pt.get_pt_pk2d(COSMO, TRS['TI'], ptc=PTC,
+                                           update_ptc=False)
+
+    COSMO2 = ccl.Cosmology(
+        Omega_c=COSMO["Omega_c"], Omega_b=COSMO["Omega_b"], h=COSMO["h"],
+        sigma8=COSMO["sigma8"]+0.05, n_s=COSMO["n_s"],
+        transfer_function='bbks', matter_power_spectrum='linear')
+
+    pee2_no_update = ccl.nl_pt.get_pt_pk2d(COSMO2, TRS['TI'], ptc=PTC,
+                                           update_ptc=False)
+    pee2 = ccl.nl_pt.get_pt_pk2d(COSMO2, TRS['TI'], ptc=PTC)
+
+    assert pee1.eval(0.1, 0.9, COSMO) == pee1_no_update.eval(0.1, 0.9, COSMO)
+    assert pee2.eval(0.1, 0.9, COSMO) != pee2_no_update.eval(0.1, 0.9, COSMO2)