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Re: log expression not simplified


Thanks to everybody contributing to this thread. In particular to
Andrzej who turned my attention to the use of complexity functions in
mathematica's simplifying tools.

On 18 Gen, 11:53, Andrzej Kozlowski <a... at mimuw.edu.pl> wrote:

> [...]
> However, it is hard to get it to simplify the expression to -1 because th=
e only way to do so seems to involve temporarily increasing the default com=
plexity. Thus, to get it to work we need a craftily designed custom complex=
ity function, like, for example, this one:
>
> f[expr_] := -2 Count[expr, _Log, {0, Infinity}] + LeafCount[expr]
>
> This function "rewards" Simplify for expanding logs and, in this case, th=
e "incentive" works:
>
> Simplify[Log[a/b]/Log[b/a], Assumptions -> {a > 0, b > a},
>  ComplexityFunction -> f]
>
> -1
>
> [...]
>
> Andrzej Kozlowski


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