integral.cc

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/******************************************************************************
 * Copyright 2017 The Apollo Authors. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *****************************************************************************/
 
#include "modules/common/math/integral.h"
 
#include <array>
 
#include "cyber/common/log.h"
 
namespace apollo {
namespace common {
namespace math {
 
double IntegrateBySimpson(const std::vector<double>& func, const double dx,
                          const std::size_t nsteps) {
  CHECK_EQ(1U, nsteps & 1);
  double sum1 = 0.0;
  double sum2 = 0.0;
  for (std::size_t i = 1; i + 1 < nsteps; ++i) {
    if ((i & 1) != 0) {
      sum1 += func[i];
    } else {
      sum2 += func[i];
    }
  }
  return dx / 3.0 * (4.0 * sum1 + 2.0 * sum2 + func[0] + func[nsteps - 1]);
}
 
double IntegrateByTrapezoidal(const std::vector<double>& func, const double dx,
                              const std::size_t nsteps) {
  double sum = 0;
  for (std::size_t i = 1; i + 1 < nsteps; ++i) {
    sum += func[i];
  }
  return dx * sum + 0.5 * dx * (func[0] + func[nsteps - 1]);
}
 
}  // namespace math
}  // namespace common
}  // namespace apollo