From 06b4a5b105f5aebe66b987194fc9b5c207fae5ff Mon Sep 17 00:00:00 2001
From: Weiqun Zhang <WeiqunZhang@lbl.gov>
Date: Mon, 24 Feb 2025 18:41:06 -0800
Subject: [PATCH] Make Parser CI less sensitive to roundoff errors (#4321)

Replace `1-cos(x)` with `2*sin(x/2)**2` to reduce roundoff errors for
small x's.
---
 Tests/Parser/main.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Tests/Parser/main.cpp b/Tests/Parser/main.cpp
index df82ba2f3f0..aafd8da8a09 100644
--- a/Tests/Parser/main.cpp
+++ b/Tests/Parser/main.cpp
@@ -318,14 +318,14 @@ int main (int argc, char* argv[])
                         {-149.e-6}, {1.e-6}, 1000,
                         1.e-12, 1.e-15);
 
-        nerror += test1("if(z<lramp, 0.5*(1-cos(pi*z/lramp))*dens, dens)",
+        nerror += test1("if(z<lramp, sin(pi/2*z/lramp)**2*dens, dens)",
                         {{"lramp",8.e-3},{"pi",3.14},{"dens",1.e23}},
                         {"z"},
                         [=] (Real z) -> Real {
                             Real lramp=8.e-3, pi=3.14, dens=1.e23;
                             if (z < lramp) {
-                                //return 0.5*(1-std::cos(pi*z/lramp))*dens;
-                                return 0.5*dens-0.5*dens*std::cos(pi*z/lramp);
+                                auto x = std::sin(pi/2*z/lramp);
+                                return x*x*dens;
                             } else {
                                 return dens;
                             }