Expression rationalization gets stuck or takes too long (it worked in V9.5.1)

[OndrejBukovsky]

Describe the bug
Recently, I updated Math.js from version 9.5.1 to the latest version, and an expression rationalization that worked before doesn't work anymore. (see To Reproduce)

To Reproduce

import * as mathjs from 'mathjs';

const aa = mathjs.parse("6285.67^5/(s+6285.67)^5");
const bb = mathjs.rationalize(aa, {}, false); // It gets stuck here

console.log(bb.toString());

[josdejong]

Thanks for reporting. I played around with it and simplied the example case a bit:

math.rationalize("(x + 1)^4") // slow
math.rationalize("(x + 1)^5") // takes forever

I guess the function expands the expression into (x + 1) * (x + 1) * (x + 1) * (x + 1) * (x + 1) and then goes over all possibilities, which grows exponentially the larger the exponent is. Not sure though, just a wild guess.

Help debugging and understanding what's going on here would be welcome.

[josdejong]

Since this worked in v9.5.1, a first step can be to understand the changes in rationalize since then.

[OndrejBukovsky]

Thank you for your response. If I have time, I will try to help with the investigation.

[josdejong]

Thanks!

[gwhitney]

Can confirm, this now prevents the doc tests from running at all in #3375, as it attempts to rationalize (2x+1)^6.