jaytreiman

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16 years, 158 days

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These are questions asked by jaytreiman

A person asked me why the following code does not give the integral of (x^2+y^2)*z over the top of the unit sphere.

VectorCalculus:-SurfaceInt((x^2 + y^2)*z, [x, y, z] = Surface(<1, s, t>, s = 0 .. Pi/2, t = 0 .. 2*Pi, coords = spherical))

The correct answer is Pi/2, but Maple gives 2*(-1 + Pi)*Pi^2.

Will someonoe please explain this behavior?

I was playing with plots:-fieldplot in Maple 2019 and found that sometime the grid option gives a strange result.  The code I used was

with(plots):
fieldplot([-x/(x^2+y^2)^1.5,-y/(x^2+y^2)^1.5],x=-1..1,y=-1..1);
fieldplot([-x/(x^2+y^2)^1.5,-y/(x^2+y^2)^1.5],x=-1..1,y=-1..1,grid=[8,8]);
fieldplot([-x/(x^2+y^2)^1.5,-y/(x^2+y^2)^1.5],x=-1..1,y=-1..1,grid=[7,7]);

The first two plots come out as expected.  The third plot has (0,0) in the grid, a point where the vector field does not exist.  Rather than giving an error or ignoring the point, Maple 2019 (and 2018) plots a single arrow through the origin. The file with plots is below.  I hope that this can be changed to give a different output.

 


 

with(plots):
fieldplot([-x/(x^2+y^2)^1.5,-y/(x^2+y^2)^1.5],x=-1..1,y=-1..1);
fieldplot([-x/(x^2+y^2)^1.5,-y/(x^2+y^2)^1.5],x=-1..1,y=-1..1,grid=[8,8]);
fieldplot([-x/(x^2+y^2)^1.5,-y/(x^2+y^2)^1.5],x=-1..1,y=-1..1,grid=[7,7]);

 

 

 

 


 

Download fieldplots_1.mw

Does anyone know why png is not listed in the help on plot/devices?  The png device exists and works.

Also, are there any other unlisted plot devices?

I have a test server up for MapleTA 8.  Where is the option to show a student's name on the questions?

I tried to use multiple light sources with transparency for 3D plots and could not get it to work.  There are indications in the plot,structure help that this is supposed to be possible.  I have attached a worksheet that demonstrates some of the problems with the "light" and "LIGHT" options for 3D plotting.  Much of the output has been removed since the graphics take so much space.  The same plots are generated in both Windows and Linux.

Does anyone...

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