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Incorrect reduction

Posted 1 year ago
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Is there an incorrect theorem embedded in wolfram alpha, or is this a bug? See image.

Any time I enter " (i (2 x^* - 1))/(2 (x^* - 1) x^* ) " it reduces to "i / x^* " I need to show an equivalence, but when this is on the right hand side of the equation, it reduces to this " i/x^* " nonsense. Any ideas? I see why it's doing it (order of operations), but it's wrong.

enter image description here

14 Replies

Here's an example...

enter image description here

Incorrect reduction

Common factors are cancelled (standard in rational function fields). Think of it as a removable singularity, one that, well, got removed.

(2 (5 - I 7) - 1) is not the same as 2 ((5 - I 7) - 1)

Daniel, you might want to look at this again. Look at my numerical example I provided. Then go ahead and enter the same calculation using just x instead of the complex conjugate of x. It won’t cancel in either of these, for the same reason it shouldn’t for the former. It’s inconsistent.

Ah, yes. Bad precedence. I filed a bug report for this.

Thanks, and here's a visual just in case.

enter image description here

And Gustavo is right'o! But not exactly as I entered it.

Okay, weird...just narrowed it down. In my first image I didn't include the equation as I entered it. It's a bug in how it's reading my input. Take a look at this image now, as it includes what I actually type.

enter image description here

The temporary work around is to put additional parenthesis around the 2 x^* in the numerator.

I am confused. What is x^* ?

X^* means complex conjugate of X.

I understand now.

X^* is interpreted as the complex conjugate in natural language, but it is a syntax error in Mathematica.

Yep. Seems that way.

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