Plotting a function not working correctly

04132015, 03:46 PM
(This post was last modified: 04132015 03:46 PM by Ollie.)
Post: #1




Plotting a function not working correctly
Hey!
I've been experimenting and finding roots of polynomials graphically but today I came across a weird glitch. I tried to plot the following function: 0.1x^5 + 1.3x^4  x^3  15x^2  8x  1, a function that has 5 different roots. The problem is that I cannot see the line that is supposed to cross the xaxis for the first time, all I see are very sparsely scattered dots instead of a continuous line. Has anyone else come across such a problem before on the Prime? If so, have you found a fix for it? 

04132015, 04:32 PM
Post: #2




RE: Plotting a function not working correctly
(04132015 03:46 PM)Ollie Wrote: Hey! Check your plot settings. Press [Shift][Plot] to open the plot settings, and look at the second page of settings (use the menu option at the bottom of the screen to get to different pages of settings). Graph 3D  QPI  SolveSys 

04132015, 06:56 PM
Post: #3




RE: Plotting a function not working correctly
(04132015 03:46 PM)Ollie Wrote: Hey! Plots ok on my Prime. You have to zoom in on the xaxis quite a bit to see where the curve crosses the axis. As Han suggested, check your plot settings to make sure your plot style is either fixed step segments or Adaptivenot fixed step dots. 

04182015, 11:43 AM
Post: #4




RE: Plotting a function not working correctly
Unfortunately I'm still having problems with this.
I can see all the other intersections but there's one missing at x ~ 12.91 Settings: The more I go up the more lonely single dots I can see on the curve. :/ 

04182015, 12:05 PM
Post: #5




RE: Plotting a function not working correctly
(04182015 11:43 AM)Ollie Wrote: Unfortunately I'm still having problems with this.Nothing really new to me here... Note that the 50g does a perfect job here, just much slower. 

04182015, 12:09 PM
Post: #6




RE: Plotting a function not working correctly
(04182015 12:05 PM)Tugdual Wrote: Nothing really new to me here... Note that the 50g does a perfect job here, just much slower. Are you trying to say that this is intended and not a bug/glitch of some sort? Because if it is then that's just outright dumb, even my TI84 can graph the function perfectly without leaving any lonely dots on the curve. 

04182015, 12:19 PM
Post: #7




RE: Plotting a function not working correctly
(04182015 12:09 PM)Ollie Wrote:I don't think it is intended, I'm just meant that it is a glitch I have seen a long time ago and was never fixed.(04182015 12:05 PM)Tugdual Wrote: Nothing really new to me here... Note that the 50g does a perfect job here, just much slower. 

04182015, 12:50 PM
Post: #8




RE: Plotting a function not working correctly
Hi,
If you use the Advanced Graphing, you will see the correct graph, but this is very long and not very practicaly. All my TI calculator can graph this fonction correctly! Marcel 

04182015, 02:49 PM
Post: #9




RE: Plotting a function not working correctly
I'll ch k this out when I get home.
In the meantime, try out solve(), zeros() and fsolve() in CAS which should all give you solutions quickly. 

04182015, 04:52 PM
Post: #10




RE: Plotting a function not working correctly
Hi,
It looks like to be able to see the whole part of the graph that includes all roots, you need to set the xrange to include all roots, and the yrange to be at least the max/min of your polynomial over the selected xrange. In this case x from 15 to 15 and y from 100 to 100 seem to work. An estimate for the xrange can be easily found (Lagrange). 

04182015, 05:38 PM
Post: #11




RE: Plotting a function not working correctly
(04182015 04:52 PM)Alberto Candel Wrote: Hi, Ooh, It works! It seems like the calculator sort of dismisses the parts that go outside your x and yranges but setting the correct ranges fixes it. Kinda annoying, but I guess we can live with it. Thanks! 

04192015, 12:23 AM
(This post was last modified: 04192015 05:50 AM by Alberto Candel.)
Post: #12




RE: Plotting a function not working correctly
The max of your polynomial over the range of the roots (like 15<x<3) is not larger than 3000, but the plot shows the relevant part (the 5 roots) with a yrange setting of about +/100.


« Next Oldest  Next Newest »

User(s) browsing this thread: 1 Guest(s)