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relayman35712-Amethyst
12-Amethyst
November 19, 2023
Solved

odd result when plotting offset circle

  • November 19, 2023
  • 1 reply
  • 1321 views

This isn't urgent, I'm just curious here, but in the attached Prime 8.0 file I'm plotting an offset circle in steps from 0° to 360°.  When I reduce the resolution by going to 10° steps I get the interesting figure on the right.  Why is that happening?  

 

 

Picture1.png

Best answer by Werner_E

1) In your sheet you set line style to "none" so we possibly won't see what your picture shows.

 

2) You don't show HOW you would manage a step width of 10°. If you do it correctly, you will see exactly what you expect.
Here with Line Style set to full line:

Werner_E_0-1700431053022.png

I guess you just used

Werner_E_1-1700431102758.png

which would explain what you posted.

That way there still is created a vector with 361 elements!!

Werner_E_2-1700431294328.png

But only elements #0,10,20,... get the values you intend, the rest is filled with zeros by default.

 

You may consider using something like

Werner_E_3-1700431609568.png

 

or

 

Werner_E_5-1700431946644.png

 

A less "legal" but convenient way uses the undocumented (and so unreliable) trick that an inline evaluation turns a range into a vector

Werner_E_0-1700432595775.png

Don't try to set the unit deg at the result - it will throw an error.

 

 

 

1 reply

W
Werner_E25-Diamond IAnswer
25-Diamond I
November 19, 2023

1) In your sheet you set line style to "none" so we possibly won't see what your picture shows.

 

2) You don't show HOW you would manage a step width of 10°. If you do it correctly, you will see exactly what you expect.
Here with Line Style set to full line:

Werner_E_0-1700431053022.png

I guess you just used

Werner_E_1-1700431102758.png

which would explain what you posted.

That way there still is created a vector with 361 elements!!

Werner_E_2-1700431294328.png

But only elements #0,10,20,... get the values you intend, the rest is filled with zeros by default.

 

You may consider using something like

Werner_E_3-1700431609568.png

 

or

 

Werner_E_5-1700431946644.png

 

A less "legal" but convenient way uses the undocumented (and so unreliable) trick that an inline evaluation turns a range into a vector

Werner_E_0-1700432595775.png

Don't try to set the unit deg at the result - it will throw an error.

 

 

 

R
relayman35712-AmethystAuthor
12-Amethyst
November 20, 2023

Thank you Werner!

 

1) Yes, sorry - I forgot to mention I changed i:=0,1..360 to i:=0,10..360 to go to 10 degree steps.

 

2) I didn't know i:0,10..N still produced N+1 elements. I thought it would produce N/10.

 

That undocumented trick is very interesting.  

 

Thank you for getting me back on track!

W
Werner_E25-Diamond I
25-Diamond I
November 20, 2023

 

2) I didn't know i:0,10..N still produced N+1 elements. I thought it would produce N/10.

 

 

The range "values" (actually a range is kind of an implicit loop) are used to address the vector elements.

If the range ist defined as i:=0,10..N and you assign v[i := ..., then you assign values to vector element #0, #10, #20, .... and the elements with other numbers like #3 oder #12 are left undefined and so Prime sets them to zero. You can't expect that with i=10 Prime assign the value to vector element #1.

When you write v[20:=123 you create a vector with 21 elements. element #20 holds the value 123 and the elements from #0 to #19 are set to 0.

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