Problem definition

• Operators on unknowns/kernels
  • Available differential operators
  • The DifferentialOperator class
  • The Operand class
  • The OperatorOnUnknown class
  • The OperatorOnUnknowns class
  • The LcOperatorOnUnknown class
  • The LcOperatorOnUnknowns class
  • The OperatorOnKernel class
  • The KernelOperatorOnUnknowns class
  • The TensorKernel class
• H-matrices
  • Cluster tree
  • Approximate matrix