# Re: Inversion of an algorithm

*From*: Patricia Shanahan <pats@xxxxxxx>*Date*: Tue, 21 Apr 2009 06:10:41 -0700

Daniel Pitts wrote:

Jean Guillaume Pyraksos wrote:....Hi !Not all functions, let alone algorithms, have an inverse. Therefor it is impossible to find it automatically.

Say I have a one-one function f from a set A to a set B. I have

an algorithm to compute f.

Has anyone worked on getting *automatically* an algorithm for the

inverse function from B to A ? Or is there a deep result about that ?

Has this problem something to do with automatic differentiation ?

f is *not* specifically a math function, but a recursive one on trees.

Thanks for any pointer,

JG

Remember the OP restricted the discussion to one-one functions, and

subsequent discussions effectively limited it to bijections - the

inverse is required only where it exists.

Patricia

.

**References**:**Inversion of an algorithm***From:*Jean Guillaume Pyraksos

**Re: Inversion of an algorithm***From:*Daniel Pitts

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