ScalableBField.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2016-2020 CERN for the benefit of the Acts project
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#pragma once

#include "Acts/Definitions/Algebra.hpp"
#include "Acts/MagneticField/MagneticFieldContext.hpp"
#include "Acts/MagneticField/MagneticFieldProvider.hpp"

namespace ActsExamples {

struct ScalableBFieldContext {
  Acts::ActsScalar scalor = 1.;
};

class ScalableBField final : public Acts::MagneticFieldProvider {
 public:
  struct Cache {
    Acts::ActsScalar scalor = 1.;

    Cache(const Acts::MagneticFieldContext& mctx) {
      scalor = mctx.get<const ScalableBFieldContext>().scalor;
    }
  };

  explicit ScalableBField(Acts::Vector3 B) : m_BField(std::move(B)) {}

  ScalableBField(Acts::ActsScalar Bx = 0, Acts::ActsScalar By = 0,
                 Acts::ActsScalar Bz = 0)
      : m_BField(Bx, By, Bz) {}

  Acts::Result<Acts::Vector3> getField(
      const Acts::Vector3& /*position*/,
      MagneticFieldProvider::Cache& gCache) const override {
    Cache& cache = gCache.get<Cache>();
    return Acts::Result<Acts::Vector3>::success(m_BField * cache.scalor);
  }

  Acts::Result<Acts::Vector3> getFieldGradient(
      const Acts::Vector3& /*position*/, Acts::ActsMatrix<3, 3>& /*derivative*/,
      MagneticFieldProvider::Cache& gCache) const override {
    Cache& cache = gCache.get<Cache>();
    return Acts::Result<Acts::Vector3>::success(m_BField * cache.scalor);
  }

  Acts::MagneticFieldProvider::Cache makeCache(
      const Acts::MagneticFieldContext& mctx) const override {
    return Acts::MagneticFieldProvider::Cache::make<Cache>(mctx);
  }

  bool isInside(const Acts::Vector3& /*position*/) const { return true; }

  void setField(double Bx, double By, double Bz) { m_BField << Bx, By, Bz; }

  void setField(const Acts::Vector3& B) { m_BField = B; }

 private:
  Acts::Vector3 m_BField;
};  // namespace BField

}  // namespace ActsExamples