TimeStepping.cpp

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#include "TimeStepping.h"
 
#include "tarch/Assertions.h"
#include "tarch/la/la.h"
 
 
 
std::pair<double,double> exahype2::getInterpolationWeights( double oldTimeStampOnFace, double newTimeStampOnFace, double cellTimeStamp ) {
  static tarch::logging::Log _log( "exahype2" );
 
  double timeSpan = newTimeStampOnFace - oldTimeStampOnFace;
  assertion4( tarch::la::greaterEquals(timeSpan,0.0), timeSpan, oldTimeStampOnFace, newTimeStampOnFace, cellTimeStamp );
  if ( tarch::la::equals(timeSpan,0.0) ) {
    logDebug( "getInterpolationWeights(double,double,double)", "time span equals zero" );
    return std::pair<double,double>(0.0,1.0);
  }
  else {
    double newWeight = (cellTimeStamp - oldTimeStampOnFace) / timeSpan;
 
    assertion5( tarch::la::greaterEquals(newWeight,0.0), newWeight, timeSpan, oldTimeStampOnFace, newTimeStampOnFace, cellTimeStamp );
    assertion5( tarch::la::smallerEquals(newWeight,1.0), newWeight, timeSpan, oldTimeStampOnFace, newTimeStampOnFace, cellTimeStamp );
 
    logDebug( "getInterpolationWeights(double,double,double)", "timeSpan" << timeSpan );
 
    return std::pair<double,double>(1.0-newWeight,newWeight);
  }
}
 
 
double exahype2::discretiseAndTruncateTimeStepSizes(
  double cellTimeStepSize,
  double maxGlobalTimeStepSize,
  int    discretisationStepsSize
) {
  static tarch::logging::Log _log( "exahype2" );
 
  if (tarch::la::greater(maxGlobalTimeStepSize,0.0) and cellTimeStepSize>maxGlobalTimeStepSize*3.0) {
    logDebug(
      "discretiseAndTruncateTimeStepSizes(double,double,int)",
      "truncate cell time step size from " << cellTimeStepSize << " due to max global dt=" << maxGlobalTimeStepSize
    );
    cellTimeStepSize = maxGlobalTimeStepSize*3.0;
  }
 
  if (discretisationStepsSize<=0) {
    return cellTimeStepSize;
  }
 
  static double maxCurrentTimeStepSize = -1.0;
 
  if (maxCurrentTimeStepSize<=0.0) {
    maxCurrentTimeStepSize = cellTimeStepSize;
  }
  else if (maxGlobalTimeStepSize>maxCurrentTimeStepSize) {
    maxCurrentTimeStepSize *= 3.0;
  }
 
  double result = maxCurrentTimeStepSize;
  while (result > cellTimeStepSize) {
    result /= 3.0;
  }
 
  if (discretisationStepsSize>1) {
    const double incrementOnThisLevel = result / discretisationStepsSize;
 
    do {
      result += incrementOnThisLevel;
    } while (result<cellTimeStepSize);
    result -= incrementOnThisLevel;
  }
 
  logDebug( "discretiseAndTruncateTimeStepSizes(double,double,int)", "reduce dt=" << cellTimeStepSize << " to " << result );
  return result;
}