Scatter plot is noisy when 'Smoothed Line' is OFF

[nmpixel]

Hello! Could the experts here can help with a strange Excel behavior related to graphing? The basic question: why do scatter plots appear rough or noisy for simple functions like y=sin(x) or y = mx+b when the ‘Smoothed Line’ option is OFF?

The screenshots show a few basic functions.. y = sin(x) and y = 0.8x + 0.5. The line width is set to 0 and markers removed for clarity. With that, the the roughness or ‘noise’ is easily visible. This roughness disappears completely when the Smoothed Line option is switched ON, but why is there such a high degree of roughness when the option is OFF?

At first I thought this was due to the IEE 754 floating point standard that limits Excel to 15 digits. But now I’m not so sure, because the degree of roughness in these graphs would represent error in the 5^th, 6^th, or 7^th decimal place, not the 15^th.

If interested, try this quick test. Create a column of x values 0, 0.02, 0.04 and another with sin(x). Then plot a scatter plot with Smoothed Line OFF and zoom in close. You should see this same jitter or noise.

Ideas?
Thanks!

sin(x) and mx+b
file:///Users/Michael/Documents/Screenshots/Screen%20Shot%202018-03-11%20at%208.51.20%20PM.png

two equations for circle → sin/cos and y=SQRT(100-x^2)
file:///Users/Michael/Documents/Screenshots/Screen%20Shot%202018-03-11%20at%2010.00.59%20PM.png

 

[shg]

Create a column of x values 0, 0.02, 0.04 and another with sin(x)

I don't see any noise in that.

file:///Users/Michael/...

You can't upload pictures from your 'puter -- you need to put them on a photo sharing site.

 

[nmpixel]

Thanks for responding shp. I appreciate it!

I uploaded the photos on a photosharing site, but the resulting URL contains too much personal information. If there is another display error (that I cannot edit in the post afterward), then the information will be forever emblazoned here. Thus, I posted this question at another Excel forum because the pictures are crucial to explain the problem. Please look there if possible.

 

[Fluff]

Cross posted https://www.excelforum.com/excel-ch...r-plots-are-noisy-with-smoothed-line-off.html

Cross-Posting
In future please provide links to any other threads (see rule 13 here along with the explanation: Forum Rules).
This way, other members can see what has already been done in regards to a question, and do not waste time working on a question that may already be answered.

 

[nmpixel]

Apologies. The other post is at ExcelForum.com with the same title "scatter plots are noisy when Smoothed Line in OFF". I would not have cross-posted - and had no plan to do so - but I could not post pictures or edit my post here.


https://www.excelforum.com/excel-ch...r-plots-are-noisy-with-smoothed-line-off.html