josdejong/mathjs

simplify("(x^2)^0.5") should be "abs(x)"

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#3,329 创建于 2024年11月29日

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 (5 评论) (0 反应) (0 负责人)JavaScript (13,832 star) (1,298 fork)batch import
bughelp wanted

描述

While there are genuine use cases when returning "x" would be better (that's what most humans would expect), strictly speaking it is incorrect.

To reproduce in the mathnotepad:

derivative("(x^2)^0.5", "x").evaluate({x:-3})
    1

derivative("(x^2)^0.5", "x", {simplify:false}).evaluate({x:-3})
    -1

Here I evaluate the same derivative at the same point x=-3 but get two different results. Same problem for x^4 and I assume all other even powers.

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javascript
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backendapi
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bug
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clear
前置要求
JavaScriptbasic algebra
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70
研究方向
Look at the simplify function in mathjs, particularly the rules for exponent simplification. The issue is that (x^2)^0.5 currently simplifies to x, but should be abs(x) to ensure correctness for negative x. Given that the derivative evaluation gives different results, this is a bug. Check simplify.js and the combsimp logic. Consider adding a rule that converts (x^n)^(1/m) to abs(x)^(n/m) when n is even and m is odd. There are 5 comments that may contain additional context or proposed approaches.
simplify("(x^2)^0.5") should be "abs(x)" · josdejong/mathjs#3329 | Good First Issue