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We have the fourier-transform:

$$F\{f\}(w) = \int_{-\infty}^\infty f(x)\exp(iwx)dx$$

Which has extremely many applications and interpretations throughout science and engineering. For instance since it has the famous convolution rule: $$F(f*g) = F(f)\cdot F(g)$$ which can be used to speed up convolutions, it also has special differentiation and integration rules: $$F\left\{\frac{\partial f}{\partial x}\right\}(w) = wiF\{f\}(w)$$ $$F\left\{\int f\right\}(w) = \frac{F\{f\}(w)}{iw}$$ making it very useful in solving differential equations.


So I have thought about what happens if we replace the complex exponential with a logarithm:

$$L\{f\}(w) = \int_{0}^\infty f(x)\log(wx)dx$$

Do you think this would make sense to investigate? Could it have any interesting properties? Are there any other integral transforms involving logarithms which are interesting or useful?


EDIT Observation by Tom-Tom, we can rewrite it as:

$$\int_0^\infty f(x)\log(\omega x)\mathrm dx= \left(\int_0^\infty f(x)\mathrm dx\right)\log(\omega) +\int_0^\infty f(x)\log(x)\mathrm dx = a \log(w) + b$$ with constants: $a$ is the integral of $f$ and $b$ is a log-weighted integral of $f$.

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    $\begingroup$ One of the key in Fourier transforms is that derivatives are transformed into product by $\mathrm i\omega$ and convolutions into products of transforms. $\endgroup$
    – Tom-Tom
    Jan 5, 2016 at 13:35
  • $\begingroup$ Yes you are right, I can add that to the description in the question if you want. $\endgroup$ Jan 5, 2016 at 13:36
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    $\begingroup$ Another remark : $$\int_0^\infty f(x)\log(\omega x)\mathrm dx= \left(\int_0^\infty f(x)\mathrm dx\right)\log(\omega) +\int_0^\infty f(x)\log(x)\mathrm dx.$$ Seeing this, your attempt for transform is just of function of the form $a\log(\omega)+b$. $\endgroup$
    – Tom-Tom
    Jan 5, 2016 at 13:42
  • $\begingroup$ Thanks for the help. Do you think it could get more interesting if we put a function of $w$ as upper limit of the integral? $\endgroup$ Jan 5, 2016 at 14:04
  • $\begingroup$ I think you should first clearly chose the properties of the transformation that you want. $\endgroup$
    – Tom-Tom
    Jan 5, 2016 at 14:07

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