how to get the mathematical function sin

[picster]

Never mind, I discovered the answer with a little impromptu LCDing.

What is unclear in the manual is that the angle in degrees is represented by a value of 0-255 instead of 0-359. It's NOT in radians as the manual suggests (where a decimal value of 6.28 radians would correspond to 360 degrees). To calculate the value to pass to the function SIN x, you have to use x=255y/360 where y was your angle in degrees.

The result returned from the SIN function is in the range of 0-255, in two's compliment form (where 0-127 corresponds to a scaled sin result of 0.00 to 1.00 respectively and 128-255 corresponds to a scaled sin result of -1.00 to 0.00 respectively).

Although it's not super accurate, it's reasonably adequate to 2 decimal places if you figure 0-127 scaling is better than 1 to 100.

[mackrackit]

The results are in
Binary Radians as the manual suggest...

[picster]

The results are in
Binary Radians as the manual suggest...

If I'm not mistaken, the results of a sin function are merely a ratio and don't have a unit. In this case, it's -127 to 127, which is as I see it, a number to be divided by 127 to get the actual result.

Radians are a unit like degrees, and the result wouldn't be in radians anyway, since the result is merely supposed to be a ratio.

I could be way off base with this, and would be glad to be shown how radians are involved.

picster

[mackrackit]

It is just a way to have a circle fit into a byte. Probably should have been named something different.

http://www.oopic.com/pgchap15.htm

[picster]

It is just a way to have a circle fit into a byte. Probably should have been named something different.

http://www.oopic.com/pgchap15.htm

Interesting link. Sorry, I don't mean to nit-pic, just to provide some clarification.

From a mathematical standpoint, "Brads" as referred to in the link, is a suggested misnomer as well, since radians play no role in the user's-end of the equation. Lacking any other existing unit, some new unit should be assigned. Since the nature of any angle measurement is that it cycles, similarities in this respect are moot point (since it's a requirement). I'm kind of partial to "Bangles", myself - Binary Angles where there are 256 units in a full cycle.

The difficulties I encountered while trying to implement SIN properly in my recent program was due to the fact that the manual provided no examples, and the wording was such that one would think that radians (by definition) were the actual unit of measurement (which they aren't, since the function doesn't repeat every 6.28 units). I hope this helps others who are trying to successfully implement this function.

picster

[mackrackit]

I do not see any buttheads or nit-picers...
I see a confusing subject being discussed.

I agree that some if not most of the examples are lacking, that is part of the reason the wiki was started.

Would you be game to writing an article about this for the math section?
http://www.picbasic.co.uk/forum/content.php?r=163

[rsocor01]

Although it's not super accurate, it's reasonably adequate to 2 decimal places if you figure 0-127 scaling is better than 1 to 100.

The PBP SIN function is accurate enough for most applications. It has an accuracy of 1/256 per Sine cycle. Of course, if you are trying to make a calculator like Minssss is trying to do it won't be accurate enough.

Robert