[HP Prime] Plots containing complex numbers bug?


Plot the following expression in the Function app:


The resulting plot is only partialy shown... values should be plotted for x < -3 as well. I assume this has something to do with the way the Prime handles exact/inexact arithmatic?

Both Mathematica and a textbook confirm the plot should display values for x < -3

I'll try to remember to upload a screen shot when I get storage space on this site.


I've plotted the expression two ways (working horizontally in the figure):

The first row shows the Mathematica output, the Prime equation, and Prime output. Same for the second row, just rewrote the expression. Both Prime plots seem to disagree with Mathematica's plot.

Edited: 4 Dec 2013, 2:54 p.m. after one or more responses were posted


What if you plot:

3 NTHROOT X *((X+3)/(3 NTHROOT (X+3)))


Not sure how to enter that? Do I use tick marks or something?


Update... Found yet another way the Prime graphs this function:


I see you learned how to use NTHROOT.

The lower-right result is somewhat similar to the Complex-valued plot that you get from Wolfram Alpha except the plot is in the wrong quadrant for -3 < x < 0.



I haven't looked into using NTHROOT yet...

What's even weirder... if you download the "Xcas Pad" android app and plot the original function above, you get Wolfram's correct plot! The Xcas Pad app is built on xcas... go figure?

Regardless; I don't feel very confident this plot system is up to the task. I'd rather have no plot than a wrong plot.

Edited: 4 Dec 2013, 9:19 p.m.


I'm guessing the 48 series is also deficient since it does exactly the same thing? :-)

It really gets down to the behavior in the HP math library. NTHROOT (x v/ y) returns the real root, and fractional power will return the principal root instead of the real one.

Its probably time to update that I think. No reason not to have the behavior dependent on the complex flag.

If you'd like to see some graphs that wolfram totally screws up, I've got a nice collection. There really is no "magic bullet" for graphing. :-)




The main problem is that you are using mathematical functions (^ to a non integer, or NTHROOT) which happends NOT TO BE FUNCTIONS by the strict definition of the word function.

ie: these 'function' have multiple mathematicaly correct results and various math system are giving you different (correct) results, which results in a different output plot.

Furthemore, depending on the complex setting of Prime, you can get different graphs on the same machine!


Possibly Related Threads...
Thread Author Replies Views Last Post
  Sending little images to the Prime (...and Program name bug?) Erwin Ried 19 1,799 12-10-2013, 05:35 PM
Last Post: Erwin Ried
  HP Prime: complex numbers in CAS. Alberto Candel 1 464 12-06-2013, 02:36 PM
Last Post: parisse
  [HP Prime] plotfunc() bug in CAS Chris Pem10 2 539 12-04-2013, 02:46 PM
Last Post: Chris Pem10
  HP Prime Spreadsheet Copy bug Michael de Estrada 1 466 12-03-2013, 11:34 PM
Last Post: Walter B
  HP Prime Matrix TERRIBLE bug and question uklo 19 1,582 11-25-2013, 12:10 PM
Last Post: Mic
  HP Prime graphing bug BruceH 1 399 11-19-2013, 08:14 AM
Last Post: Joe Horn
  Complex Number Entry on Prime Jeff O. 19 1,647 11-16-2013, 12:34 PM
Last Post: Jeff O.
  [Prime] Shutdown timer bug? Cristian Arezzini 2 394 11-16-2013, 10:34 AM
Last Post: Cristian Arezzini
  HP Prime: Linear Solver app bug BruceH 0 265 11-15-2013, 06:36 PM
Last Post: BruceH
  Possible bug with sqrt function in the HP prime Michael de Estrada 6 631 11-15-2013, 12:49 PM
Last Post: Michael de Estrada

Forum Jump: