RegionPlot of annulus gives a mesh












1












$begingroup$


So I tried plotting an annulus in two ways:



RegionPlot[Annulus[{0,0},{a,b}]]

Graphics[Annulus[{0,0},{a,b}]]


Why does RegionPlot give a fractal looking thing? (see below for when a=1; b=5;)
RegionPlot image



*note, I used wolfram programing lab.






graphics regions







share|improve this question











$endgroup$












  • $begingroup$
    What are $a$ and $b$ here?
    $endgroup$
    – mjw
    5 hours ago










  • $begingroup$
    Try a=1; b=5; But really any values give something weird
    $endgroup$
    – Ion Sme
    5 hours ago






  • 4




    $begingroup$
    Because it discretized the region in order to plot it, and it is showing the underlying triangulation mesh.
    $endgroup$
    – MarcoB
    5 hours ago






  • 1




    $begingroup$
    @IonSme I guess they just use different defaults for plotting; the Graphics result is "normal-looking" though.
    $endgroup$
    – MarcoB
    5 hours ago






  • 2




    $begingroup$
    There are some subtle differences going on how Mma shows Regions and RegionPlot Graphics. Also Regions can be defined analytically via ImplicitRegion or ParametricRegion or as 'flat' MeshRegions. DiscretizeRegion converts every type to a MeshRegion and some functions like RegionPlot might use something similar to DiscretizeRegion under the hood to make plotting easier, whose discretization it for some reason decides to show. Like others wrote you can use ImplicitRegion to get a different (not discretized) look in your case.
    $endgroup$
    – Thies Heidecke
    4 hours ago


















1












$begingroup$


So I tried plotting an annulus in two ways:



RegionPlot[Annulus[{0,0},{a,b}]]

Graphics[Annulus[{0,0},{a,b}]]


Why does RegionPlot give a fractal looking thing? (see below for when a=1; b=5;)
RegionPlot image



*note, I used wolfram programing lab.






graphics regions







share|improve this question











$endgroup$












  • $begingroup$
    What are $a$ and $b$ here?
    $endgroup$
    – mjw
    5 hours ago










  • $begingroup$
    Try a=1; b=5; But really any values give something weird
    $endgroup$
    – Ion Sme
    5 hours ago






  • 4




    $begingroup$
    Because it discretized the region in order to plot it, and it is showing the underlying triangulation mesh.
    $endgroup$
    – MarcoB
    5 hours ago






  • 1




    $begingroup$
    @IonSme I guess they just use different defaults for plotting; the Graphics result is "normal-looking" though.
    $endgroup$
    – MarcoB
    5 hours ago






  • 2




    $begingroup$
    There are some subtle differences going on how Mma shows Regions and RegionPlot Graphics. Also Regions can be defined analytically via ImplicitRegion or ParametricRegion or as 'flat' MeshRegions. DiscretizeRegion converts every type to a MeshRegion and some functions like RegionPlot might use something similar to DiscretizeRegion under the hood to make plotting easier, whose discretization it for some reason decides to show. Like others wrote you can use ImplicitRegion to get a different (not discretized) look in your case.
    $endgroup$
    – Thies Heidecke
    4 hours ago
















1












1








1





$begingroup$


So I tried plotting an annulus in two ways:



RegionPlot[Annulus[{0,0},{a,b}]]

Graphics[Annulus[{0,0},{a,b}]]


Why does RegionPlot give a fractal looking thing? (see below for when a=1; b=5;)
RegionPlot image



*note, I used wolfram programing lab.






graphics regions







share|improve this question











$endgroup$




So I tried plotting an annulus in two ways:



RegionPlot[Annulus[{0,0},{a,b}]]

Graphics[Annulus[{0,0},{a,b}]]


Why does RegionPlot give a fractal looking thing? (see below for when a=1; b=5;)
RegionPlot image



*note, I used wolfram programing lab.






graphics regions




graphics regions






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 4 hours ago









MarcoB

38.1k556114




38.1k556114










asked 5 hours ago









Ion SmeIon Sme

876




876












  • $begingroup$
    What are $a$ and $b$ here?
    $endgroup$
    – mjw
    5 hours ago










  • $begingroup$
    Try a=1; b=5; But really any values give something weird
    $endgroup$
    – Ion Sme
    5 hours ago






  • 4




    $begingroup$
    Because it discretized the region in order to plot it, and it is showing the underlying triangulation mesh.
    $endgroup$
    – MarcoB
    5 hours ago






  • 1




    $begingroup$
    @IonSme I guess they just use different defaults for plotting; the Graphics result is "normal-looking" though.
    $endgroup$
    – MarcoB
    5 hours ago






  • 2




    $begingroup$
    There are some subtle differences going on how Mma shows Regions and RegionPlot Graphics. Also Regions can be defined analytically via ImplicitRegion or ParametricRegion or as 'flat' MeshRegions. DiscretizeRegion converts every type to a MeshRegion and some functions like RegionPlot might use something similar to DiscretizeRegion under the hood to make plotting easier, whose discretization it for some reason decides to show. Like others wrote you can use ImplicitRegion to get a different (not discretized) look in your case.
    $endgroup$
    – Thies Heidecke
    4 hours ago




















  • $begingroup$
    What are $a$ and $b$ here?
    $endgroup$
    – mjw
    5 hours ago










  • $begingroup$
    Try a=1; b=5; But really any values give something weird
    $endgroup$
    – Ion Sme
    5 hours ago






  • 4




    $begingroup$
    Because it discretized the region in order to plot it, and it is showing the underlying triangulation mesh.
    $endgroup$
    – MarcoB
    5 hours ago






  • 1




    $begingroup$
    @IonSme I guess they just use different defaults for plotting; the Graphics result is "normal-looking" though.
    $endgroup$
    – MarcoB
    5 hours ago






  • 2




    $begingroup$
    There are some subtle differences going on how Mma shows Regions and RegionPlot Graphics. Also Regions can be defined analytically via ImplicitRegion or ParametricRegion or as 'flat' MeshRegions. DiscretizeRegion converts every type to a MeshRegion and some functions like RegionPlot might use something similar to DiscretizeRegion under the hood to make plotting easier, whose discretization it for some reason decides to show. Like others wrote you can use ImplicitRegion to get a different (not discretized) look in your case.
    $endgroup$
    – Thies Heidecke
    4 hours ago


















$begingroup$
What are $a$ and $b$ here?
$endgroup$
– mjw
5 hours ago




$begingroup$
What are $a$ and $b$ here?
$endgroup$
– mjw
5 hours ago












$begingroup$
Try a=1; b=5; But really any values give something weird
$endgroup$
– Ion Sme
5 hours ago




$begingroup$
Try a=1; b=5; But really any values give something weird
$endgroup$
– Ion Sme
5 hours ago




4




4




$begingroup$
Because it discretized the region in order to plot it, and it is showing the underlying triangulation mesh.
$endgroup$
– MarcoB
5 hours ago




$begingroup$
Because it discretized the region in order to plot it, and it is showing the underlying triangulation mesh.
$endgroup$
– MarcoB
5 hours ago




1




1




$begingroup$
@IonSme I guess they just use different defaults for plotting; the Graphics result is "normal-looking" though.
$endgroup$
– MarcoB
5 hours ago




$begingroup$
@IonSme I guess they just use different defaults for plotting; the Graphics result is "normal-looking" though.
$endgroup$
– MarcoB
5 hours ago




2




2




$begingroup$
There are some subtle differences going on how Mma shows Regions and RegionPlot Graphics. Also Regions can be defined analytically via ImplicitRegion or ParametricRegion or as 'flat' MeshRegions. DiscretizeRegion converts every type to a MeshRegion and some functions like RegionPlot might use something similar to DiscretizeRegion under the hood to make plotting easier, whose discretization it for some reason decides to show. Like others wrote you can use ImplicitRegion to get a different (not discretized) look in your case.
$endgroup$
– Thies Heidecke
4 hours ago






$begingroup$
There are some subtle differences going on how Mma shows Regions and RegionPlot Graphics. Also Regions can be defined analytically via ImplicitRegion or ParametricRegion or as 'flat' MeshRegions. DiscretizeRegion converts every type to a MeshRegion and some functions like RegionPlot might use something similar to DiscretizeRegion under the hood to make plotting easier, whose discretization it for some reason decides to show. Like others wrote you can use ImplicitRegion to get a different (not discretized) look in your case.
$endgroup$
– Thies Heidecke
4 hours ago












1 Answer
1






active

oldest

votes


















4












$begingroup$

 a = 1; b = 5;


Please try plotting with Region. These look okay to me:



 Region[RegionDifference[Disk[{0, 0}, b], Disk[{0, 0}, a]]]


enter image description here



 Region[Annulus[{0, 0}, {a, b}]]


enter image description here



Here is a decent plot, with RegionPlot:



 RegionPlot[x^2 + y^2 > 1 && x^2 + y^2 < 25, {x, -6, 6}, {y, -6, 6}]


enter image description here



Here it is (again) with Graphics:



 Graphics[{LightBlue, Annulus[{0, 0}, {a, b}]}]


enter image description here






share|improve this answer











$endgroup$













  • $begingroup$
    Hmmm, that worked, but why is RegionPlot so funky?
    $endgroup$
    – Ion Sme
    5 hours ago






  • 1




    $begingroup$
    I think MarcoB mostly answers this below your question. So we can then ask: Why does RegionPlot use one algorithm, and Region another? RegionPlot seems to like functions as inputs, and also likes to have the $x$ and $y$ ranges speciifed ...
    $endgroup$
    – mjw
    5 hours ago












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1 Answer
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active

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1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









4












$begingroup$

 a = 1; b = 5;


Please try plotting with Region. These look okay to me:



 Region[RegionDifference[Disk[{0, 0}, b], Disk[{0, 0}, a]]]


enter image description here



 Region[Annulus[{0, 0}, {a, b}]]


enter image description here



Here is a decent plot, with RegionPlot:



 RegionPlot[x^2 + y^2 > 1 && x^2 + y^2 < 25, {x, -6, 6}, {y, -6, 6}]


enter image description here



Here it is (again) with Graphics:



 Graphics[{LightBlue, Annulus[{0, 0}, {a, b}]}]


enter image description here






share|improve this answer











$endgroup$













  • $begingroup$
    Hmmm, that worked, but why is RegionPlot so funky?
    $endgroup$
    – Ion Sme
    5 hours ago






  • 1




    $begingroup$
    I think MarcoB mostly answers this below your question. So we can then ask: Why does RegionPlot use one algorithm, and Region another? RegionPlot seems to like functions as inputs, and also likes to have the $x$ and $y$ ranges speciifed ...
    $endgroup$
    – mjw
    5 hours ago
















4












$begingroup$

 a = 1; b = 5;


Please try plotting with Region. These look okay to me:



 Region[RegionDifference[Disk[{0, 0}, b], Disk[{0, 0}, a]]]


enter image description here



 Region[Annulus[{0, 0}, {a, b}]]


enter image description here



Here is a decent plot, with RegionPlot:



 RegionPlot[x^2 + y^2 > 1 && x^2 + y^2 < 25, {x, -6, 6}, {y, -6, 6}]


enter image description here



Here it is (again) with Graphics:



 Graphics[{LightBlue, Annulus[{0, 0}, {a, b}]}]


enter image description here






share|improve this answer











$endgroup$













  • $begingroup$
    Hmmm, that worked, but why is RegionPlot so funky?
    $endgroup$
    – Ion Sme
    5 hours ago






  • 1




    $begingroup$
    I think MarcoB mostly answers this below your question. So we can then ask: Why does RegionPlot use one algorithm, and Region another? RegionPlot seems to like functions as inputs, and also likes to have the $x$ and $y$ ranges speciifed ...
    $endgroup$
    – mjw
    5 hours ago














4












4








4





$begingroup$

 a = 1; b = 5;


Please try plotting with Region. These look okay to me:



 Region[RegionDifference[Disk[{0, 0}, b], Disk[{0, 0}, a]]]


enter image description here



 Region[Annulus[{0, 0}, {a, b}]]


enter image description here



Here is a decent plot, with RegionPlot:



 RegionPlot[x^2 + y^2 > 1 && x^2 + y^2 < 25, {x, -6, 6}, {y, -6, 6}]


enter image description here



Here it is (again) with Graphics:



 Graphics[{LightBlue, Annulus[{0, 0}, {a, b}]}]


enter image description here






share|improve this answer











$endgroup$



 a = 1; b = 5;


Please try plotting with Region. These look okay to me:



 Region[RegionDifference[Disk[{0, 0}, b], Disk[{0, 0}, a]]]


enter image description here



 Region[Annulus[{0, 0}, {a, b}]]


enter image description here



Here is a decent plot, with RegionPlot:



 RegionPlot[x^2 + y^2 > 1 && x^2 + y^2 < 25, {x, -6, 6}, {y, -6, 6}]


enter image description here



Here it is (again) with Graphics:



 Graphics[{LightBlue, Annulus[{0, 0}, {a, b}]}]


enter image description here







share|improve this answer














share|improve this answer



share|improve this answer








edited 5 hours ago

























answered 5 hours ago









mjwmjw

1,17610




1,17610












  • $begingroup$
    Hmmm, that worked, but why is RegionPlot so funky?
    $endgroup$
    – Ion Sme
    5 hours ago






  • 1




    $begingroup$
    I think MarcoB mostly answers this below your question. So we can then ask: Why does RegionPlot use one algorithm, and Region another? RegionPlot seems to like functions as inputs, and also likes to have the $x$ and $y$ ranges speciifed ...
    $endgroup$
    – mjw
    5 hours ago


















  • $begingroup$
    Hmmm, that worked, but why is RegionPlot so funky?
    $endgroup$
    – Ion Sme
    5 hours ago






  • 1




    $begingroup$
    I think MarcoB mostly answers this below your question. So we can then ask: Why does RegionPlot use one algorithm, and Region another? RegionPlot seems to like functions as inputs, and also likes to have the $x$ and $y$ ranges speciifed ...
    $endgroup$
    – mjw
    5 hours ago
















$begingroup$
Hmmm, that worked, but why is RegionPlot so funky?
$endgroup$
– Ion Sme
5 hours ago




$begingroup$
Hmmm, that worked, but why is RegionPlot so funky?
$endgroup$
– Ion Sme
5 hours ago




1




1




$begingroup$
I think MarcoB mostly answers this below your question. So we can then ask: Why does RegionPlot use one algorithm, and Region another? RegionPlot seems to like functions as inputs, and also likes to have the $x$ and $y$ ranges speciifed ...
$endgroup$
– mjw
5 hours ago




$begingroup$
I think MarcoB mostly answers this below your question. So we can then ask: Why does RegionPlot use one algorithm, and Region another? RegionPlot seems to like functions as inputs, and also likes to have the $x$ and $y$ ranges speciifed ...
$endgroup$
– mjw
5 hours ago


















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