A mathematical expression which describe Gauss theorem can be written in following form:

(7) |

Where is a vector field, is whole body volume and is body surface. Let us rewrite it in a case of two dimensional object:

(8) |

Where is body field, is any vector field and is body edge. If we assume then because of:

(9) |

and

(10) |

we will get a simple expression which describe body field value (our "volume" calculated in the code):

(11) |