Editing Circular reference (section)

==In spreadsheets==
Circular references also occur in [[spreadsheet]]s when two cells require each other's result.  For example, if the value in Cell A1 is to be obtained by adding 5 to the value in Cell B1, and the value in Cell B1 is to be obtained by adding 3 to the value in Cell A1, no values can be computed.  (Even if the specifications are A1:=B1+5 and B1:=A1-5, there is still a circular reference.  It does not help that, for instance, A1=3 and B1=-2 would satisfy both formulae, as there are infinitely many other possible values of A1 and B1 that can satisfy both instances.)

Circular reference in worksheets can be a very useful technique for solving implicit equations such as the [[Colebrook equation]] and many others, which might otherwise require tedious [[Newton-Raphson]] algorithms in VBA or use of macros.<ref>{{cite web | title=Solve Implicit Equations Inside Your Worksheet By Anilkumar M, Dr Sreenivasan E and Dr Raghunathan K | url=http://www.frpdesigns.com/iteration.htm | access-date=2009-06-25 | archive-url=https://web.archive.org/web/20090817224237/http://www.frpdesigns.com/iteration.htm | archive-date=2009-08-17 | url-status=dead }}.</ref>

A distinction should be made with processes containing a circular reference between those that are incomputable and those that are an iterative calculation with a final output.  The latter may fail in spreadsheets not equipped to handle them but are nevertheless still logically valid.<ref name=Fiengo/>