Refactor field function and improve readability

Refactored field function to use static constexpr for constants and improved readability. Updated condition checks to use std::abs.

Author: njacazio

Detectors/Upgrades/ALICE3/macros/ALICE3Field.C

@@ -11,43 +11,41 @@
 //
 // Author: J. E. Munoz Mendez jesus.munoz@cern.ch
 
+#include <functional>
+#include <cmath>
+#include <TCanvas.h>
+#include <TH2F.h>
+#include <TStyle.h>
+
 std::function<void(const double*, double*)> field()
 {
   return [](const double* x, double* b) {
-    double Rc;
-    double R1;
-    double R2;
-    double B1;
-    double B2;
-    double beamStart = 500.;    //[cm]
-    double tokGauss = 1. / 0.1; // conversion from Tesla to kGauss
-
-    bool isMagAbs = true;
+    // RADIUS
+    static constexpr double Rc = 170.; // [cm] — R_out_coil per Ian DetectorConstruction.cc; confirmed by A. Ortiz definition
+    static constexpr double R1 = 220.; // [cm]
+    static constexpr double R2 = 290.; // [cm]
 
-    // ***********************
-    // LAYOUT 1
-    // ***********************
+    // FIELD
+    static constexpr double B1 = 2.;                                  // [T]
+    static constexpr double B2 = -B1 * Rc * Rc / (R2 * R2 - R1 * R1); // [T] — B1 in numerator, confirmed by A. Ortiz Aug 2026
+    static constexpr double beamStart = 500.;                         // [cm]
+    static constexpr double tokGauss = 1. / 0.1;                      // conversion from Tesla to kGauss
 
-    // RADIUS
-    Rc = 170.; //[cm] — R_out_coil per Ian DetectorConstruction.cc; confirmed by A. Ortiz definition
-    R1 = 220.; //[cm]
-    R2 = 290.; //[cm]
+    static constexpr bool isMagAbs = true;
 
     // To set the B2
-    B1 = 2.;                                    //[T]
-    B2 = -B1 * Rc * Rc / (R2 * R2 - R1 * R1); //[T] — B1 in numerator, confirmed by A. Ortiz Aug 2026
 
-    if ((abs(x[2]) <= beamStart) && (sqrt(x[0] * x[0] + x[1] * x[1]) < Rc)) {
+    if ((std::abs(x[2]) <= beamStart) && (sqrt(x[0] * x[0] + x[1] * x[1]) < Rc)) {
       b[0] = 0.;
       b[1] = 0.;
       b[2] = B1 * tokGauss;
-    } else if ((abs(x[2]) <= beamStart) &&
+    } else if ((std::abs(x[2]) <= beamStart) &&
                (sqrt(x[0] * x[0] + x[1] * x[1]) >= Rc &&
                 sqrt(x[0] * x[0] + x[1] * x[1]) < R1)) {
       b[0] = 0.;
       b[1] = 0.;
       b[2] = 0.;
-    } else if ((abs(x[2]) <= beamStart) &&
+    } else if ((std::abs(x[2]) <= beamStart) &&
                (sqrt(x[0] * x[0] + x[1] * x[1]) >= R1 &&
                 sqrt(x[0] * x[0] + x[1] * x[1]) < R2)) {
       b[0] = 0.;
@@ -63,4 +61,52 @@ std::function<void(const double*, double*)> field()
       b[2] = 0.;
     }
   };
-}
+}
+
+void ALICE3Field()
+{
+  gStyle->SetPalette(kRainBow);
+  gStyle->SetNumberContours(255);
+
+  auto fieldFunc = field();
+  // RZ plane visualization
+  TCanvas* cRZ = new TCanvas("cRZ", "Field in RZ plane", 800, 800);
+  gPad->SetRightMargin(0.15);
+  TH2F* hRZ = new TH2F("hRZ", "Magnetic Field B_z in RZ plane;Z [m];R [m];B_{z} [kGauss]", 100, -10, 10, 100, -5, 5);
+  hRZ->SetBit(TH1::kNoStats); // disable stats box
+  for (int i = 1; i <= hRZ->GetNbinsX(); i++) {
+    const double Z = hRZ->GetXaxis()->GetBinCenter(i);
+    for (int j = 1; j <= hRZ->GetNbinsY(); j++) {
+      const double R = hRZ->GetYaxis()->GetBinCenter(j);
+      const double pos[3] = {R * 100, 0, Z * 100}; // convert to cm
+      double b[3] = {0, 0, 0};
+      fieldFunc(pos, b);
+      hRZ->SetBinContent(i, j, b[2]);
+    }
+  }
+
+  hRZ->GetZaxis()->SetRangeUser(-30, 30);
+  hRZ->Draw("COLZ");
+  cRZ->Update();
+
+  // XY plane visualization
+  TCanvas* cXY = new TCanvas("cXY", "Field in XY plane", 800, 800);
+  gPad->SetRightMargin(0.15);
+  TH2F* hXY = new TH2F("hXY", "Magnetic Field B_z in XY plane;X [m];Y [m];B_{z} [kGauss]", 100, -5, 5, 100, -5, 5);
+  hXY->SetBit(TH1::kNoStats); // disable stats box
+
+  for (int i = 1; i <= hXY->GetNbinsX(); i++) {
+    const double X = hXY->GetXaxis()->GetBinCenter(i);
+    for (int j = 1; j <= hXY->GetNbinsY(); j++) {
+      const double Y = hXY->GetYaxis()->GetBinCenter(j);
+      const double pos[3] = {X * 100, Y * 100, 0}; // convert to cm
+      double b[3] = {0, 0, 0};
+      fieldFunc(pos, b);
+      hXY->SetBinContent(i, j, b[2]);
+    }
+  }
+
+  hXY->GetZaxis()->SetRangeUser(-30, 30);
+  hXY->Draw("COLZ");
+  cXY->Update();
+}