* The number of nodes can change, contrary to renumberCells().
* A given epsilon specifies a threshold of error in case of two nodes are merged but
* the difference of values on these nodes are higher than \a eps.
* This method performs a part of job of renumberNodes(), excluding node renumbering
* in mesh. The reasonable use of this
* method is only for multi-field instances lying on the same mesh to avoid a
* The number of nodes can change, contrary to renumberCells().
* A given epsilon specifies a threshold of error in case of two nodes are merged but
* the difference of values on these nodes are higher than \a eps.
* This method performs a part of job of renumberNodes(), excluding node renumbering
* in mesh. The reasonable use of this
* method is only for multi-field instances lying on the same mesh to avoid a