[Insight-users] AdvanceOneStep in Class GradientDescentOptimizer(itkGradientDescentOptimizer.cpp)

[庄吓海(Xiahai Zhuang)]

/**
 * Advance one Step following the gradient direction
 */
  typedef Array< double>              ParametersType;
 ParametersType m_currentPosition;
void
GradientDescentOptimizer
::AdvanceOneStep( void )
{ 

  itkDebugMacro("AdvanceOneStep");
....

  ScalesType scales = this-> GetScales();
..

  DerivativeType transformedGradient( spaceDimension ); 

  for(unsigned int j = 0; j <  spaceDimension; j++)
    {
    transformedGradient[j] = m_Gradient[j] / scales[j]; //?????????????????????? why here takes a (/scales[j])
    }                                                                            //as in method m_CostFunction-> GetValueAndDerivative(this-> GetCurrentPosition(), m_Value, m_Gradient )m_Gradient derivative
                                                                                  // m_Gradient is the derivative of MutualInformation with respect to transform parameters,
                                                                                 // why transformedGradient[j] = m_Gradient[j] / scales[j]; 
  ParametersType newPosition( spaceDimension );
  for(unsigned int j = 0; j <  spaceDimension; j++)
    {
    newPosition[j] = currentPosition[j] + 
      direction * m_LearningRate * transformedGradient[j];
    }

  this-> SetCurrentPosition( newPosition );

  this-> InvokeEvent( IterationEvent() );

}


　　　　　　　　致
礼！


　　　　　　　　庄吓海(Xiahai Zhuang)
　　　　　　　　arhye at 163.com
　　　　　　　　　　2005-05-01
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