Negative Cube Roots

Discussion about the new DM41X calculator
Post Reply
Weegie
Posts: 7
Joined: Wed Jun 09, 2021 10:28 pm

Negative Cube Roots

Post by Weegie »

First post here and only had my DM41X a week or so. Many years ago I used the HP41C in my latter college years and with my first "professional" (although I've never considered myself a professional anything). The screen eventually gave up, I really missed that calculator.

Loving the DM41 with the beautiful display and HP41 emulation it's fantastic.

Now got a DM42 on order and been trawling around watching videos and visiting blogs, forums etc: and came across this video on cube roots on the DM42 (bear with me please).

https://youtu.be/iNR7kcA08As

I thought I'd try the cube root problem on the 41 and get DATA ERROR so I tried the HP41 emulator on my computer, same result.

After all that time I never knew this was a limitation on the 41 obviously a HP limitation than a Swiss Micros problem.

I'd love to hear more from the knowledgable who are on here and will have known about this probably forever.

I'm no mathematician and a lot of the info on here is waaaay above my head.

Having a lot of fun learning though, it just intrigued me, that's all
Weegie
Posts: 7
Joined: Wed Jun 09, 2021 10:28 pm

Re: Negative Cube Roots

Post by Weegie »

Just as I posted this it struck me if the DATA ERROR is related to the 41 not natively handling complex numbers (or I don't think it can without programming). Perhaps it sees the first root as complex and can't return the value.

Of course I could be talking complete rubbish :?
grsbanks
Posts: 1122
Joined: Tue Apr 25, 2017 11:23 am
Location: Preston, Lancs, UK
Contact:

Re: Negative Cube Roots

Post by grsbanks »

It calculates the \(n\)th root of \(x\) by computing \(e^{ln(x)/n}\)

If \(x\) is negative, it can't calculate \(ln(x)\), hence the "DATA ERROR".
There are only 10 kinds of people in the world: those who understand binary and those who do not.
Weegie
Posts: 7
Joined: Wed Jun 09, 2021 10:28 pm

Re: Negative Cube Roots

Post by Weegie »

Thanks for explaining, appreciated

So finding negative roots isn't possible with the 41.

On the video I tried the test on a 48GX using the "raise to a power" to find the cube root and it returned the same answer as the DM42, but using the root finder on the 48GX returned -2.

Don't know if thats due to rounding error or if the root finder uses a different method to evaluate the root

I think I'll just try and stay clear of negative roots ;)
User avatar
Dan Simpson
Posts: 72
Joined: Wed Mar 18, 2020 3:29 pm
Location: Arizona

Re: Negative Cube Roots

Post by Dan Simpson »

Angel Martin's SandMath 4x4 Module has an x-th root of y function that allows for negative numbers.
No DM41X should be without it! ;)

https://technical.swissmicros.com/dm41x ... Latest.zip

Manual:
http://www.systemyde.com/pdf/SANDMATH_44_4x4_Manual.pdf
My Spirit animal is a Basset Hound.
My Collection: HP-55, HP-67 (Teenix Mod), HP-15C, HP-16C, HP-41CV, HP-41CX, SY41-CL (x2), DM41X (Beta), DM42, HP-42S, HP-48G, HP-71B (x2), HP-75C, HP-150.
Weegie
Posts: 7
Joined: Wed Jun 09, 2021 10:28 pm

Re: Negative Cube Roots

Post by Weegie »

Wow Dan

I just opened that zip, that contains a lot of modules.

Thankyou for the link to both the mod files and the documentation, I'm still trying to find my way around

The help is very much appreciated

John
Post Reply