Advanced Graphing App

[lrdheat]

In function app, 3 Root (x-2) plots fine. In advanced graphing app, only the part of the graph where x>2 plots. Same for (x-2)^1/3. I was looking to find the inflection point of the function in the advanced graphing app (which happens to occur at x=2). Is there a way to get the complete plot of this function in tha advanced graphing app?

[Helge Gabert]

Can't seem to be able to get that to work, either. Furthermore, 3ROOT((X-2)^2)=Y plots the whole function, but (X-2)^(2/3)=Y, again, only plots for X>=2. Actually, 3ROOT((X-2)^N)=Y plots for N even, and plots only partially for N odd.

[jte]

Something isn't right. I'll look into it.

[Helge Gabert]

Thanks so much!

[jte]

It seems to be due to excessive compiler "optimization". This can easily be an issue when relying on precise floating-point semantics. (Compiler writers have a hard time avoiding the temptation to generate machine code that doesn't precisely match up with IEEE 754 + C++ semantics.) It is a better-recognized problem now than it used to be (in the past, getting some compilers to actually produce correct floating-point code could require substantial gymnastics with the source code), so hopefully it won't be too hard to get the compiler to produce object code that better matches up with the source code.

[Nigel (UK)]

(05-18-2015 12:18 AM)lrdheat Wrote:  In function app, 3 Root (x-2) plots fine. In advanced graphing app, only the part of the graph where x>2 plots. Same for (x-2)^1/3. I was looking to find the inflection point of the function in the advanced graphing app (which happens to occur at x=2). Is there a way to get the complete plot of this function in tha advanced graphing app?

The reason it doesn't work with powers (e.g., (x-2)^(1/3)) is that a fractional power of a negative number is in general complex. If you try working out (-2)^1/3 from the keyboard (in Home) you'll either get an error or a complex result, if "Allow complex results from real input" is ticked. This is as it should be: forcing (-2)^(1/3) to be real would mean an extra discontinuity (a cut) in the function in the complex plane.

I thought that the nthroot function (e.g., 3 nthroot (-2)) was intended to get around this. It gives a real result in the Home screen, but not in the Advanced Function app - a bug, perhaps?

Apologies if this is obvious!

Nigel (UK)