Prefer Std::Numbers::PI

We have C++20 now and can use the portable alternative to spelling
out the value or using the Posix-only 'M_PI' macro.

examples/known_answer_test.cpp

@@ -70,6 +70,7 @@
 #include <cmath>
 #include <iomanip>
 #include <iostream>
+#include <numbers>
 #include <stdexcept>
 #include <string>
 #include <vector>
@@ -82,13 +83,13 @@ namespace {
 
     double u(const Vec& x)
     {
-        const double pi = 3.14159265358979323846264338327950288;
+        constexpr auto pi = std::numbers::pi;
         return std::sin(2*pi*x[0]) * std::cos(2*pi*x[1]) * x[2];
     }
 
     double Lu(const Vec& x)
     {
-        const double pi = 3.14159265358979323846264338327950288;
+        constexpr auto pi = std::numbers::pi;
         return -2 * 2*pi * 2*pi * std::sin(2*pi*x[0]) * std::cos(2*pi*x[1]) * x[2];
     }
 

examples/upscale_elasticity.cpp

@@ -49,6 +49,7 @@
 #include <ctime>
 #include <fstream>
 #include <iostream>
+#include <numbers>
 #include <sstream>
 #include <stdexcept>
 #include <string>
@@ -58,10 +59,6 @@
 
 using namespace Opm::Elasticity;
 
-#ifndef M_PI
-#define M_PI std::acos(-1.0)
-#endif
-
 //! \brief Display the available command line parameters
 void syntax(char** argv)
 {
@@ -176,7 +173,7 @@ void parseCommandLine(int argc, char** argv, Params& p)
   if (method == "none")
     p.method = UPSCALE_NONE;
   p.Emin     = param.getDefault<double>("Emin",0.0);
-  p.dip      = param.getDefault<double>("dip_angle", M_PI/2);
+  p.dip      = param.getDefault<double>("dip_angle", std::numbers::pi/2);
   p.azimuth  = param.getDefault<double>("azimuth_angle", 0.0);
   p.ctol     = param.getDefault<double>("ctol",1.e-6);
 #ifndef HAVE_OLD_CPGRID_API

opm/elasticity/boundarygrid.cpp

@@ -20,6 +20,7 @@
 #include <cmath>
 #include <cstddef>
 #include <iostream>
+#include <numbers>
 #include <vector>
 
 namespace Opm {
@@ -281,8 +282,8 @@ bool BoundaryGrid::cubicSolve(double eps, double A, double B, double C,
     if (W <= -epsmall && P < 0) {
       double FI = acos(-Q/sqrt(-P*P*P));
       X.push_back( 2*std::sqrt(-P)*std::cos(FI/3));
-      X.push_back(-2*std::sqrt(-P)*std::cos((FI+M_PI)/3));
-      X.push_back(-2*std::sqrt(-P)*std::cos((FI-M_PI)/3));
+      X.push_back(-2*std::sqrt(-P)*std::cos((FI+std::numbers::pi)/3));
+      X.push_back(-2*std::sqrt(-P)*std::cos((FI-std::numbers::pi)/3));
     } else if (std::fabs(W) < epsmall && Q < 0) {
       X.push_back(2*std::pow(-Q,1.f/3));
       X.push_back(-.5f*X[0]);

opm/porsol/common/BoundaryPeriodicity.hpp

@@ -27,6 +27,7 @@
 #include <algorithm>
 #include <array>
 #include <iostream>
+#include <numbers>
 #include <vector>
 
 namespace Opm
@@ -65,11 +66,11 @@ namespace Opm
 	}
 
     private:
-	double cmpval() const
-	{
-            const double pi = 3.14159265358979323846264338327950288;
-	    return centroid[(canon_pos/2 + 1)%3] + pi*centroid[(canon_pos/2 + 2)%3];
-	}
+        double cmpval() const
+        {
+            return centroid[(canon_pos/2 + 1)%3]
+                +  std::numbers::pi*centroid[(canon_pos/2 + 2)%3];
+        }
     };