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'[OT] Mathematical question'
1999\12\05@022211 by Quentin

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This might seem waaay OT but there is a PIC in there somewhere.
Can somebody please help this rusted brain:

I've been given information as such:
if x=0, y=0
x=15, y=0.259
30, 0.5
45, 0.707
60, 0.866
75, 0.966
90, 1.000

You will see that while X is linear, Y is not (Log??). With these
information available, how would I calculate Y for all the other values
of X?

I want to use it in a lookup table in the PIC.

Thanks
Quentin

1999\12\05@025156 by Russell McMahon

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Quentin,

What you want depends on whether your question is specific or general and
how accurate you want the result.
What you have described is the results for Y = Sin(X)
X in degrees.

You can calculate this using a Sin function.
If you are using assembler such routines are available.
If you are using C or BASIC or some other high level language then the
function is (probably) already available in the language.

If this is a general question then the normal method is "interpolation".
Linear interpolation is the simplest form of this and generally the least
accurate but may be OK for your purpose.

Before we go into this it would be useful for you to provide some more
information eg
- Are you after Sin (as shown here) or is the question more general?
- What accuracy do you need?
- What is the application?



regards



     Russell McMahon
_____________________________

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Help the hungry at no cost to yourself!
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(* - or woman, child or internet enabled intelligent entity :-))


From: Quentin <spam_OUTqscTakeThisOuTspamICON.CO.ZA>

{Quote hidden}

1999\12\05@031323 by Harold Hallikainen

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On Sun, 5 Dec 1999 09:24:25 +0200 Quentin <.....qscKILLspamspam@spam@ICON.CO.ZA> writes:
>This might seem waaay OT but there is a PIC in there somewhere.
>Can somebody please help this rusted brain:
>
>I've been given information as such:
>if x=0, y=0
>x=15, y=0.259
>30, 0.5
>45, 0.707
>60, 0.866
>75, 0.966
>90, 1.000
>
>You will see that while X is linear, Y is not (Log??). With these
>information available, how would I calculate Y for all the other
>values
>of X?
>
>I want to use it in a lookup table in the PIC.


       Well, I HAVE done a 7th order power series by solving 7 equations with 7
unknowns (the coefficients).  It worked, but was a lot of trouble.
       Last time, I used a standard curve fitting program (Curve Expert).  Jack
Crenshaw mentions a bunch of them in the December issue of Embedded
Systems Programming.  Here are the ones he lists:

http://www.micromath.com/scientist.html
http://www.spss.com
http://www.ebicom.net/~dhyams/cvxpt.htm


Harold

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1999\12\05@075715 by andy howard

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> This might seem waaay OT but there is a PIC in there somewhere.
> Can somebody please help this rusted brain:

> I've been given information as such:
> if x=0, y=0
> x=15, y=0.259
> 30, 0.5
> 45, 0.707
> 60, 0.866
> 75, 0.966
> 90, 1.000

> You will see that while X is linear, Y is not (Log??). With these
> information available, how would I calculate Y for all the other values
> of X?

This is a sine function. Y = sin(X). You can do it on your calculator or
look it up in a book of tables.

> I want to use it in a lookup table in the PIC.

Somewhere I've seen a application that does exactly this to generate a
pseudo-sine wave for audio testing.  If I can find it I'll post a pointer.





.

1999\12\06@001815 by Joseph Rutsky

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This is the sin function.

Quentin wrote:

{Quote hidden}

1999\12\06@030135 by Dr. Imre Bartfai

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Hi,

the equation is: y =  sin(x)

I hope this helps.

Imre


On Sun, 5 Dec 1999, Quentin wrote:

{Quote hidden}

1999\12\06@055851 by Quentin

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Thanks All
Told you my brain is rusted.

Quentin

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