use multiple angle formula for sin/cos in sneut

neutrinos/sneut5.H

@@ -824,21 +824,28 @@ void nu_photo(const sneutf_t& sf,
 
     Real taudt = nu_constants::iln10 * sf.tempi;
 
-    // equation 3.7, compute the expensive trig functions only one time
-
-    Real cos1 = std::cos(nu_constants::fac1 * tau);
-    Real cos2 = std::cos(nu_constants::fac1 * 2.0e0_rt * tau);
-    Real cos3 = std::cos(nu_constants::fac1 * 3.0e0_rt * tau);
-    Real cos4 = std::cos(nu_constants::fac1 * 4.0e0_rt * tau);
-    Real cos5 = std::cos(nu_constants::fac1 * 5.0e0_rt * tau);
-    Real last = std::cos(nu_constants::fac2 * tau);
-
-    Real sin1 = std::sin(nu_constants::fac1*tau);
-    Real sin2 = std::sin(nu_constants::fac1*2.0e0_rt*tau);
-    Real sin3 = std::sin(nu_constants::fac1*3.0e0_rt*tau);
-    Real sin4 = std::sin(nu_constants::fac1*4.0e0_rt*tau);
-    Real sin5 = std::sin(nu_constants::fac1*5.0e0_rt*tau);
-    Real xast = std::sin(nu_constants::fac2*tau);
+    // equation 3.7
+
+    const Real [cos1, sin1] = amrex::sincos(nu_constants::fac1 * tau);
+
+    // double, triple, etc. angle formulas
+    // sin/cos (2 fac1 tau)
+    const Real sin2 = 2.0_rt * sin1 * cos1;
+    const Real cos2 = 2.0_rt * cos1 * cos1 - 1.0_rt;
+
+    // sin/cos (3 fac1 tau)
+    const Real sin3 = 3.0_rt * sin1 - 4.0_rt * sin1 * sin1 * sin1;
+    const Real cos3 = 4.0_rt * cos1 * cos1 - cos1 - 3.0_rt * cos1;
+
+    // sin/cos (4 fac1 tau) -- use double angle on sin2/cos2
+    const Real sin4 = 2.0_rt * sin2 * cos2;
+    const Real cos4 = 2.0_rt * cos2 * cos2 - 1.0_rt;
+
+    // sin/cos (5 fac1 tau)
+    const Real sin5 = 5.0_rt * sin1 - 20.0_rt * sin1 * sin1 * sin1 + 16.0_rt * sin1 * sin1 * sin1 * sin1 * sin;
+    const Real cos5 = 16.0_rt * cos1 * cos1 * cos1 * cos1 * cos1 - 20.0_rt * cos1 * cos1 * cos1 + 5.0_rt * cos1;
+
+    const Real [xast, last] = amrex::sincos(fac2 * tau);
 
     Real a0 = 0.5e0_rt * c00
         + c01 * cos1 + dd01 * sin1 + c02 * cos2 + dd02 * sin2