Given two rectangles, and a maximum difference score, tell me whether the aspect ratio of these rectangles are considered similar or not?
For example a $2\times4$ rectangle [ratio $0.5$] and a $2\times3$ [ratio $0.66$] are considered similar, meaning that the difference of $0.16$ is still considered similar.
Also a $4\times2$ rectangle [ratio $2$] and a $3\times2$ rectangle [ratio $1.5$] are both considered similar and the difference is $0.5$ which is much larger than $0.16$ and yet is considered similar.
Another example of a $3\times2.9$ rectangle and a $2.8\times3.1$ rectangle are also considered similar.
How can one give one formula for calculating such a thing?
Further clarification
Let us represent a completely identical ratio with a score of $0$, meaning that there is no change between them
Let's represent a completely different ratio with a score of $1$
Let's say that the largest rectangle can be up to $1000$ width or up to $1000$ height
Example of the same ratio: $2\times3$ rectangle and $4\times6$ rectangle and the like
An example of a completely different ratio: a $1\times1000$ rectangle and a $1000\times1$ rectangle
There is no mathematical definition for the similarity of aspect ratios. You might consider the ratio of the aspect ratios as a measure of aspect ratio similarity. The closer to $1$ the more similar.
You could then choose a cutoff point for "similar enough", depending on your application.