Trig Ratios: What Function Does "sin(x)" Represent?

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Discussion Overview

The discussion revolves around the mathematical representation and computational methods of the sine function, specifically what the expression sin(x) signifies when evaluated. It touches on theoretical aspects, computational algorithms, and the use of series expansions.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about the function represented by sin(x) when evaluated, seeking clarity on its mathematical basis.
  • Another participant proposes a series expansion for sin(x) involving a summation of terms, suggesting a finite order reduction to the interval [-π; π].
  • A different participant expresses a belief that calculators and computers traditionally use Taylor's series for sine and cosine functions, but mentions being informed that modern calculations rely on the CORDIC algorithm.
  • One participant acknowledges the cleverness of the algorithm and expresses doubt about the series expansion, indicating a connection to Fast Fourier Transform (FFT) but notes that CORDIC is simpler.
  • Another participant expresses appreciation for the information shared in the discussion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the primary computational method used for evaluating sin(x), with differing views on the use of Taylor's series versus the CORDIC algorithm. The discussion remains unresolved regarding the preferred approach.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the computational methods and the specific contexts in which each method is applied. The scope of the series expansion and its convergence properties are not fully explored.

Gaz031
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I've been working with the trigonometric ratios for a long time now and was wondering, when you type sin(x), where x is any number and hit the equals sign, what function is actually being applied to the number?
 
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I guess that would be
[tex]\sin(x)=\sum_n \left( \frac{x^{4n+1}}{(4n+1)!}-\frac{x^{4n+3}}{(4n+3)!} \right)[/tex]
to finite order, by first reducing to the fundamental [tex][-\pi;\pi][/tex]
 
For a very long time, I thought that calculators (and computers) used the Taylor's series (what humanino gives is a variation on that) for ex, sin(x), cos(x), etc. but I have been informed that all modern calculations use the "CORDIC" algorithm.

Here is a link to an explanatory website:
http://www.dspguru.com/info/faqs/cordic.htm
 
Last edited by a moderator:
now, that's clever ! Anyway, I had doubt about the series. Thanks Hallsoflvt. This algorithm makes me thinf of FFT.
edit:
(well actually it is much simpler)
 
Interesting, thanks.
 

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