Calculator giving weird answers?

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    Calculator Ti-83 Weird
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Discussion Overview

The discussion revolves around the unexpected outputs from calculators when evaluating the sine function at multiples of pi, particularly focusing on the TI-83 Plus and other models. Participants explore the implications of floating-point arithmetic and rounding errors in computational devices.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that their TI-83 calculator returns -2^-13 for sin(4pi), which is close to 0, while other multiples of pi return 0.
  • Another participant confirms similar results on their TI-83+, with sin(6pi) returning 2E-13 and sin(8pi) returning -4E-13, while their TI-36X Pro shows 0.
  • A participant mentions graphing sin(x) on their calculator and still receiving -2E-13 for x = 4pi.
  • One participant attributes the issue to floating-point arithmetic, suggesting that the calculators may be limited in their internal binary arithmetic precision.
  • Another participant speculates that the calculator first computes 4*pi, which introduces rounding errors before calculating the sine value.
  • A participant shares their experience of testing multiples of pi on their TI-83 Plus and expresses curiosity about the results, indicating they will continue their exploration.

Areas of Agreement / Disagreement

Participants generally agree on the occurrence of rounding errors and floating-point arithmetic issues, but there is no consensus on the exact cause or implications of the results observed.

Contextual Notes

Limitations include the potential for rounding errors in floating-point calculations and the dependence on the specific calculator models used, which may have different internal representations of numbers.

1MileCrash
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For sin(4pi), my calculator gives -2^-13.

Obviously, that is really close to the correct value of 0, but it just says 0 for ANY other multiple of pi I've tried.

Weird right?

TI-83 plus.. common calculator. Anyone have issues like this?
 
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Ha! Just tried it on my TI-83+ (from 1997), and it shows the same thing. Says the same for Sin4pi. Sin6pi returns 2E-13, and sin8pi returns -4E-13.

My TI-36X Pro, which I use almost exclusively now, returns 0.
 
Yep, I get those same results as you, never tried those, so my capital ANY was not a very meaningful "ANY," heh.

When it showed this error, I actually decided to graph "sin x" on it, then find the value when x = 4pi.. still returns -2e-13 that way.

Weird.
 
Welcome to the joys of floating point arithmetic.
 
hmmmm transcendentals likely calculated by a series...


and 10-13 is about 1/(2^43)

i'm guessing their internal binary arithmetic is good to ~43 bits.
Anybody got an old HP31?

old jim
 
It must be doing the 4*pi calculation first, incorporates some rounding error, then takes the sin of that.
 
Moonbear said:
It must be doing the 4*pi calculation first, incorporates some rounding error, then takes the sin of that.

But it works fine for something like pi/2 or even 10pi.
 
Try 8 pi.
 
um, so, I was kind of bored this evening and I saw this thread. Since I love excel and graphs... and numbers, I just started punching multiples of pi into my TI- 83 Plus calculator and noting down the results from 1pi to 100pi.

I got these graphs

the first is the whole shebang, the second is a zoom in on the first portion of the graph

it's interesting I guess, but I don't know enough about calculators to have any idea of why it does it like this. I'm going to keep going, since I have nothing else to do tonight, and see what happens on out from 100pi.

also there is the excel file if anyone feels like looking at the numbers and messing with them
 

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