# Re: Determining the inverse function operation from a function definition

## SM Ryan <wyrmwif@tsoft.org>

28 Apr 2005 14:54:06 -0400

*From comp.compilers*

| List of all articles for this month |

**From: ** | SM Ryan <wyrmwif@tsoft.org> |

**Newsgroups: ** | comp.compilers |

**Date: ** | 28 Apr 2005 14:54:06 -0400 |

**Organization: ** | Quick STOP Groceries |

**References: ** | 05-04-067 |

**Keywords: ** | theory |

**Posted-Date: ** | 28 Apr 2005 14:54:06 EDT |

# It "feels" as though the inverse operation could be accomplished by

# backing-out the original operation steps in reverse order, but it appears

# that such an approach could also be fraught with peril.

Function inversion is simple in affine functions, after dealing with

issues like f(x)=0. The problem for these kinds of functions is

equivalent to inverting a matrix, which may or may not be singular. If

the function is not affine but is differentiable, then it is locally

affine; you can see if you can invert the differential matrix. Again

be aware of potential singularities.

Prolog does symbolic inversion on some functions.

Some function inversions are thought to be inherently difficult;

cryptography is based on this assumption. For example DES is an

invertible function that is intentionally hard to invert.

# I'd appreciate it if someone could point me to some relevant material.

http://www.google.com/search?rls=en-us&q=function+inversion

Results 1 - 10 of about 1,370,000 for function inversion. (0.35 seconds)

--

SM Ryan http://www.rawbw.com/~wyrmwif/

OOOOOOOOOO! NAVY SEALS!

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