Complex Conformal Mapping












1












$begingroup$


I'm trying to prove that the mapping



$Z=z^m$



for $m geq dfrac 12$, transforms the region $r geq 0$, $0leqthetaleqdfrac{pi}{m}$ into the upper half plane $Ygeq 0$ where $Z=X+iY.$



My attempt was to write



$z=re^{itheta}$ so that




$$z^m = r^mbigg[cos(theta m) + isin(theta m)bigg],$$




and the upper-half region would be controlled by $operatorname{Im}(z)$, so




$$operatorname{Im}(z^m) = r^m sin(pi)=r^mk$$




so that $k in [0,1].$



I feel like I am missing why $m$ must be $ geq dfrac 12.$



Any help is appreciated.










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$endgroup$












  • $begingroup$
    I think it has to do with your angle range: $0lethetalepi/m.$ If, say, $m=1/4,$ then you'd be double-covering the complex plane with the inequality $0lethetale4pi.$
    $endgroup$
    – Adrian Keister
    Jan 8 at 14:14










  • $begingroup$
    Yes my thoughts! Thanks for your comment Adrian!
    $endgroup$
    – kroneckerdel69
    Jan 8 at 15:03
















1












$begingroup$


I'm trying to prove that the mapping



$Z=z^m$



for $m geq dfrac 12$, transforms the region $r geq 0$, $0leqthetaleqdfrac{pi}{m}$ into the upper half plane $Ygeq 0$ where $Z=X+iY.$



My attempt was to write



$z=re^{itheta}$ so that




$$z^m = r^mbigg[cos(theta m) + isin(theta m)bigg],$$




and the upper-half region would be controlled by $operatorname{Im}(z)$, so




$$operatorname{Im}(z^m) = r^m sin(pi)=r^mk$$




so that $k in [0,1].$



I feel like I am missing why $m$ must be $ geq dfrac 12.$



Any help is appreciated.










share|cite|improve this question











$endgroup$












  • $begingroup$
    I think it has to do with your angle range: $0lethetalepi/m.$ If, say, $m=1/4,$ then you'd be double-covering the complex plane with the inequality $0lethetale4pi.$
    $endgroup$
    – Adrian Keister
    Jan 8 at 14:14










  • $begingroup$
    Yes my thoughts! Thanks for your comment Adrian!
    $endgroup$
    – kroneckerdel69
    Jan 8 at 15:03














1












1








1





$begingroup$


I'm trying to prove that the mapping



$Z=z^m$



for $m geq dfrac 12$, transforms the region $r geq 0$, $0leqthetaleqdfrac{pi}{m}$ into the upper half plane $Ygeq 0$ where $Z=X+iY.$



My attempt was to write



$z=re^{itheta}$ so that




$$z^m = r^mbigg[cos(theta m) + isin(theta m)bigg],$$




and the upper-half region would be controlled by $operatorname{Im}(z)$, so




$$operatorname{Im}(z^m) = r^m sin(pi)=r^mk$$




so that $k in [0,1].$



I feel like I am missing why $m$ must be $ geq dfrac 12.$



Any help is appreciated.










share|cite|improve this question











$endgroup$




I'm trying to prove that the mapping



$Z=z^m$



for $m geq dfrac 12$, transforms the region $r geq 0$, $0leqthetaleqdfrac{pi}{m}$ into the upper half plane $Ygeq 0$ where $Z=X+iY.$



My attempt was to write



$z=re^{itheta}$ so that




$$z^m = r^mbigg[cos(theta m) + isin(theta m)bigg],$$




and the upper-half region would be controlled by $operatorname{Im}(z)$, so




$$operatorname{Im}(z^m) = r^m sin(pi)=r^mk$$




so that $k in [0,1].$



I feel like I am missing why $m$ must be $ geq dfrac 12.$



Any help is appreciated.







complex-analysis functions complex-numbers






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share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 8 at 14:04









amWhy

1




1










asked Jan 8 at 13:02









kroneckerdel69kroneckerdel69

258




258












  • $begingroup$
    I think it has to do with your angle range: $0lethetalepi/m.$ If, say, $m=1/4,$ then you'd be double-covering the complex plane with the inequality $0lethetale4pi.$
    $endgroup$
    – Adrian Keister
    Jan 8 at 14:14










  • $begingroup$
    Yes my thoughts! Thanks for your comment Adrian!
    $endgroup$
    – kroneckerdel69
    Jan 8 at 15:03


















  • $begingroup$
    I think it has to do with your angle range: $0lethetalepi/m.$ If, say, $m=1/4,$ then you'd be double-covering the complex plane with the inequality $0lethetale4pi.$
    $endgroup$
    – Adrian Keister
    Jan 8 at 14:14










  • $begingroup$
    Yes my thoughts! Thanks for your comment Adrian!
    $endgroup$
    – kroneckerdel69
    Jan 8 at 15:03
















$begingroup$
I think it has to do with your angle range: $0lethetalepi/m.$ If, say, $m=1/4,$ then you'd be double-covering the complex plane with the inequality $0lethetale4pi.$
$endgroup$
– Adrian Keister
Jan 8 at 14:14




$begingroup$
I think it has to do with your angle range: $0lethetalepi/m.$ If, say, $m=1/4,$ then you'd be double-covering the complex plane with the inequality $0lethetale4pi.$
$endgroup$
– Adrian Keister
Jan 8 at 14:14












$begingroup$
Yes my thoughts! Thanks for your comment Adrian!
$endgroup$
– kroneckerdel69
Jan 8 at 15:03




$begingroup$
Yes my thoughts! Thanks for your comment Adrian!
$endgroup$
– kroneckerdel69
Jan 8 at 15:03










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