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#1 2006-01-26 08:09:24



Generating sines

Yesterday I wrote asking the following


I have been trying to program some sine equations.

My hope has been to create a loop of 100 iterations to generate results from 0 to 1 which has been successful

I have started with i set to 0

I have incremented it by Pi/200 stopping when i gets to Pi/2

And sin(i) has produced 0 to 1 as hoped for.

The problem is how do I generate 0 to 1 to 0 again

I have tried stopping i when it gets to pi which works very well until the final loop where I get a tiny value. Can anyone help. Am i trying the impossible?


I was asked to supply the code. Here it is

It works great but the last value I get is

Sin = 1.12246908816338e-14

when I was hoping for 0

maybe it is just a rounding problem as suggested


//100 loops to produce sin results from 0 to 1;
//trace() outputs to screen

var loopCount=0;
var desiredLoops=100;

for (var i:Number=0;i<=Math.PI;i+= Math.PI/(desiredLoops*2)){
    trace("loopCount = "+loopCount);
    trace("Sin = "+Math.sin(i));


One further question

How could I modify the code to produce

-1 to 0 to 1 to 0 to -1

#2 2006-01-26 17:55:04



Re: Generating sines

OK, that makes sense. You are incrementing a real number (one with fractional component), and the computer can't do that with total accuracy. However adding integers will be accurate. so:


for (var i=0;i<desiredLoops;i++) {
    trace("Sin = "+Math.sin(r));

I haven't included data types. "i" and "desiredLoops" should be integers, "r" a real, and you will need to be careful with "i/desiredLoops" to make sure it creates a fractional result (ie convert both to a real value before dividing).

As to the question of rising and falling values - the sin function does that anyway, so just go to higher values, something like:

r = (i/desiredLoops)*Math.PI*4;  // times 4

And you can make it start at a lower value by having something like:

r = ( (i/desiredLoops) - 0.5 )*Math.PI*4; 

Play with it! Use trace() a lot, and let us know what happens:)

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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