Author Topic: N-spire 3.1 graphing glitch  (Read 3005 times)

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Offline piexil

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N-spire 3.1 graphing glitch
« on: March 23, 2013, 12:07:28 pm »
One day, while bored in AP chemistry, I decided to just start randomly graphing things.

I started with the function f(x)=x^(sin(x)), now this graphs pretty normally on the 83/84, but on the nspire, it goes crazy while in 2D graphing mode


So I graphed i in 3d mode to see what would happen, and it comes out as it should


Hmm, I wonder if any other functions cause this too happen, and I discovered another weird one with
f(x)=x^x^x^2
2d:

3d:

« Last Edit: March 23, 2013, 03:54:02 pm by piexil »
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Offline ElementCoder

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Re: N-spire 3.1 graphing glitch
« Reply #1 on: March 23, 2013, 12:16:36 pm »
What I think is happening here is a problem with calculating. I don't know what the Nspire does exactly when plotting, but I think it makes a taylor expansion to fit the function. The taylor expansion of x^sin(x) at x=0 looks like 1+x*ln(x)+0.5*x²*ln²(x). Therefore entering negative values for x results in a calculation error. The same goes for x^x^x^2, which has a taylor expansion of x+x^3 log^2(x)+O(x^4). Probably a lot of other functions have this problem as well.
« Last Edit: March 23, 2013, 12:16:50 pm by ElementCoder »

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Offline Hayleia

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Re: N-spire 3.1 graphing glitch
« Reply #2 on: March 23, 2013, 12:34:26 pm »
(
Doesn't really answer to the topic, but piexil, you can use [img] tags to include the image in your post without users having to click on it ;)
For example, [img]http://i.imgur.com/0Nw1JxP.png[/img] gives that:

)
« Last Edit: March 23, 2013, 12:38:30 pm by Hayleia »
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Offline piexil

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Re: N-spire 3.1 graphing glitch
« Reply #3 on: March 23, 2013, 03:54:57 pm »
(
Doesn't really answer to the topic, but piexil, you can use [img] tags to include the image in your post without users having to click on it ;)
For example, [img]http://i.imgur.com/0Nw1JxP.png[/img] gives that:

)

Sweet, thanks! I haven't posted on forums in forever, so I forgot all of that.
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Offline Rhombicuboctahedron

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Re: N-spire 3.1 graphing glitch
« Reply #4 on: March 27, 2013, 07:30:34 pm »
Change your window, and it should change too. I remember graphing sin(x)/x and finding that the graph would look like a sine function, and then changing the window size and it would be correct, even when only by less than a percent of the window size would recalculate it. I assumed that the calculator just graphed a number of points and found the best fit curve, and that is why these appear differently, but I don’t know for sure.
but I think it makes a taylor expansion to fit the function.
I thought almost all ti calculators use the CORDIC algorithm