function state2 = updateStateFromConstEquation(variableName, state1, state2, equation)
  const = getVariableFromAlgebricEquation("const", state1, equation) ;
  state2add = state2 ;
  state2add.const = const ;
  state2.(variableName) = getVariableFromAlgebricEquation(variableName, state2add, equation) ;
end