An almost reverse triangle inequality involving two complex numbers

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Given two complex numbers $u$ and $v$, numerically it seems that
$$1+vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert u+vvert+vert 1+u+vverttag$*$$$
with equality holding for example when $(u=v=-1)$ Or $(u=exp(frac2ipi3),v=exp(frac4ipi3))$ but these are not the only cases.
This inequality does not follow in a clear way to me from Hlawka's inequality, but it looks some how similar to a difficult inequality
$$vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert1+uvvert$$
which was proved in this paper.
I would appreciate any idea or help in proving $(*)$.
complex-analysis inequality
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up vote
6
down vote
favorite
Given two complex numbers $u$ and $v$, numerically it seems that
$$1+vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert u+vvert+vert 1+u+vverttag$*$$$
with equality holding for example when $(u=v=-1)$ Or $(u=exp(frac2ipi3),v=exp(frac4ipi3))$ but these are not the only cases.
This inequality does not follow in a clear way to me from Hlawka's inequality, but it looks some how similar to a difficult inequality
$$vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert1+uvvert$$
which was proved in this paper.
I would appreciate any idea or help in proving $(*)$.
complex-analysis inequality
add a comment |Â
up vote
6
down vote
favorite
up vote
6
down vote
favorite
Given two complex numbers $u$ and $v$, numerically it seems that
$$1+vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert u+vvert+vert 1+u+vverttag$*$$$
with equality holding for example when $(u=v=-1)$ Or $(u=exp(frac2ipi3),v=exp(frac4ipi3))$ but these are not the only cases.
This inequality does not follow in a clear way to me from Hlawka's inequality, but it looks some how similar to a difficult inequality
$$vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert1+uvvert$$
which was proved in this paper.
I would appreciate any idea or help in proving $(*)$.
complex-analysis inequality
Given two complex numbers $u$ and $v$, numerically it seems that
$$1+vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert u+vvert+vert 1+u+vverttag$*$$$
with equality holding for example when $(u=v=-1)$ Or $(u=exp(frac2ipi3),v=exp(frac4ipi3))$ but these are not the only cases.
This inequality does not follow in a clear way to me from Hlawka's inequality, but it looks some how similar to a difficult inequality
$$vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert1+uvvert$$
which was proved in this paper.
I would appreciate any idea or help in proving $(*)$.
complex-analysis inequality
complex-analysis inequality
edited Feb 2 at 6:07
asked Jan 24 at 11:00
Omran Kouba
23.7k13579
23.7k13579
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1 Answer
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This follows from Hlawka. Denormalizing the inequality, you want to show
$$|x| + |y| + |z| leq |x+y| + |y+z| + |z+x| + |x+y+z|$$
Substitute $u = y+z, v = z+x, w = x+y$, you want to show
$$|v+w-u| + |w+u-v| + |u+v-w| leq 2(|u| + |v| + |w|) + |u+v+w|$$
But Hlawka tells you that
$$beginalign*
textRight hand side &ge (|u| + |v| + |w|) + (|u+v| + |v+w| + |w+u|) \
&= (|v+w| + |u|) + (|w+u| + |v|) + (|u+v| + |w|) \
&ge |v+w-u| + |w+u-v| + |u+v-w| \
&= textLeft hand side
endalign*$$
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
accepted
This follows from Hlawka. Denormalizing the inequality, you want to show
$$|x| + |y| + |z| leq |x+y| + |y+z| + |z+x| + |x+y+z|$$
Substitute $u = y+z, v = z+x, w = x+y$, you want to show
$$|v+w-u| + |w+u-v| + |u+v-w| leq 2(|u| + |v| + |w|) + |u+v+w|$$
But Hlawka tells you that
$$beginalign*
textRight hand side &ge (|u| + |v| + |w|) + (|u+v| + |v+w| + |w+u|) \
&= (|v+w| + |u|) + (|w+u| + |v|) + (|u+v| + |w|) \
&ge |v+w-u| + |w+u-v| + |u+v-w| \
&= textLeft hand side
endalign*$$
add a comment |Â
up vote
4
down vote
accepted
This follows from Hlawka. Denormalizing the inequality, you want to show
$$|x| + |y| + |z| leq |x+y| + |y+z| + |z+x| + |x+y+z|$$
Substitute $u = y+z, v = z+x, w = x+y$, you want to show
$$|v+w-u| + |w+u-v| + |u+v-w| leq 2(|u| + |v| + |w|) + |u+v+w|$$
But Hlawka tells you that
$$beginalign*
textRight hand side &ge (|u| + |v| + |w|) + (|u+v| + |v+w| + |w+u|) \
&= (|v+w| + |u|) + (|w+u| + |v|) + (|u+v| + |w|) \
&ge |v+w-u| + |w+u-v| + |u+v-w| \
&= textLeft hand side
endalign*$$
add a comment |Â
up vote
4
down vote
accepted
up vote
4
down vote
accepted
This follows from Hlawka. Denormalizing the inequality, you want to show
$$|x| + |y| + |z| leq |x+y| + |y+z| + |z+x| + |x+y+z|$$
Substitute $u = y+z, v = z+x, w = x+y$, you want to show
$$|v+w-u| + |w+u-v| + |u+v-w| leq 2(|u| + |v| + |w|) + |u+v+w|$$
But Hlawka tells you that
$$beginalign*
textRight hand side &ge (|u| + |v| + |w|) + (|u+v| + |v+w| + |w+u|) \
&= (|v+w| + |u|) + (|w+u| + |v|) + (|u+v| + |w|) \
&ge |v+w-u| + |w+u-v| + |u+v-w| \
&= textLeft hand side
endalign*$$
This follows from Hlawka. Denormalizing the inequality, you want to show
$$|x| + |y| + |z| leq |x+y| + |y+z| + |z+x| + |x+y+z|$$
Substitute $u = y+z, v = z+x, w = x+y$, you want to show
$$|v+w-u| + |w+u-v| + |u+v-w| leq 2(|u| + |v| + |w|) + |u+v+w|$$
But Hlawka tells you that
$$beginalign*
textRight hand side &ge (|u| + |v| + |w|) + (|u+v| + |v+w| + |w+u|) \
&= (|v+w| + |u|) + (|w+u| + |v|) + (|u+v| + |w|) \
&ge |v+w-u| + |w+u-v| + |u+v-w| \
&= textLeft hand side
endalign*$$
edited Sep 9 at 15:50
answered Sep 9 at 5:44
Pig
206113
206113
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