simplify not working correctly with conjugate?

asked 2019-09-08 18:55:07 +0100

Rutger
13 ●1 ●7

In my notebook environment when I do this :

var('v','a')
t=(I*a/2)*(v-conjugate(v))
(t**3).expand()

It gives me the correct result. However when I do :

(t**3).expand().simplify()

The answer I get is zero. Is this a bug, or is there something I don't understand about the simplify function? Additionally: Is there another, better way to simplify expressions with many conjugates?

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answered 2019-09-08 21:52:19 +0100

eric_g
8469 ●10 ●62 ●168 https://luth.obspm.fr/...

Well, it seems that when using conjugate, you have to specify that the involved symbolic variables are complex. Indeed one has

sage: (x - conjugate(x)).simplify()
0
sage: v = var('v')
sage: (v - conjugate(v)).simplify()
0

(I am a little bit puzzled by this, since I thought Sage's symbolic variables are assumed complex by default)

But

sage: v = var('v', domain='complex')
sage: (v - conjugate(v)).simplify()
v - conjugate(v)

and

sage: v = var('v')
sage: assume(v, 'complex')
sage: (v - conjugate(v)).simplify()
v - conjugate(v)

So, regarding your example, you have to use var('a', 'v', domain='complex') in the first line.

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Great, Thanks a lot!

Rutger ( 2019-09-08 22:32:52 +0100 )edit

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Asked: 2019-09-08 18:55:07 +0100

Seen: 434 times

Last updated: Sep 08 '19

simplify not working correctly with conjugate? edit