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Incorrect reduction

Jeffrey N Cook
Posted 4 years ago

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
POSTED BY: Jeffrey N Cook
14 Replies
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I understand now.

X^* is interpreted as the complex conjugate in natural language, but it is a syntax error in Mathematica.
POSTED BY: Gustavo Delfino
Jeffrey N Cook
Jeffrey N Cook
Posted 4 years ago

Yep. Seems that way.
POSTED BY: Jeffrey N Cook
Jeffrey N Cook
Jeffrey N Cook
Posted 4 years ago

X^* means complex conjugate of X.
POSTED BY: Jeffrey N Cook
Jeffrey N Cook
Jeffrey N Cook
Posted 4 years ago

The temporary work around is to put additional parenthesis around the 2 x^* in the numerator.
POSTED BY: Jeffrey N Cook

I am confused. What is x^* ?
POSTED BY: Gustavo Delfino
Jeffrey N Cook
Jeffrey N Cook
Posted 4 years ago

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
POSTED BY: Jeffrey N Cook
Jeffrey N Cook
Jeffrey N Cook
Posted 4 years ago

And Gustavo is right'o! But not exactly as I entered it.
POSTED BY: Jeffrey N Cook
Jeffrey N Cook
Jeffrey N Cook
Posted 4 years ago

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

enter image description here
POSTED BY: Jeffrey N Cook
Jeffrey N Cook
Jeffrey N Cook
Posted 4 years ago

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.
POSTED BY: Jeffrey N Cook

Ah, yes. Bad precedence. I filed a bug report for this.
POSTED BY: Daniel Lichtblau

(2 (5 - I 7) - 1) is not the same as 2 ((5 - I 7) - 1)
POSTED BY: Gustavo Delfino

Common factors are cancelled (standard in rational function fields). Think of it as a removable singularity, one that, well, got removed.
POSTED BY: Daniel Lichtblau
Jeffrey N Cook
Jeffrey N Cook
Posted 4 years ago

Incorrect reduction
POSTED BY: Jeffrey N Cook
Jeffrey N Cook
Jeffrey N Cook
Posted 4 years ago

Here's an example...

enter image description here
POSTED BY: Jeffrey N Cook
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