# Arduino Forum

## Topics => Robotics => Topic started by: Jetfire on Apr 04, 2013, 11:40 pm

Title: Inverse trig functions
Post by: Jetfire on Apr 04, 2013, 11:40 pm
They locked this topic away in the arcives, so I'll just do this:

http://arduino.cc/forum/index.php?PHPSESSID=99fdf9fb9ed775fd5c50e3e70f03aec8&topic=41402.0

I need the <math.h> library and I can't find the .h and .ccp files.
Or if you could just tell me how to get the arc functions that would work too.

Thanks.
Title: Re: Inverse trig functions
Post by: Jsut210 on Apr 05, 2013, 12:21 am
This may help http://arduino.cc/forum/index.php/topic,44229.0.html
What happens if you just try something like:

Code: [Select]
`float invsin = asin(num);`
Title: Re: Inverse trig functions
Post by: codlink on Apr 05, 2013, 12:37 am
He's trying to tell you that the math library is already including in the IDE.  And actually, you don't have to use a header to include it either. [ref]http://arduino.cc/en/Math/H

Here's another library if you need more complexity.

http://playground.arduino.cc/Main/ComplexMath
Title: Re: Inverse trig functions
Post by: robtillaart on Apr 05, 2013, 08:31 pm
note that the asin() return radians
- http://www.nongnu.org/avr-libc/user-manual/group__avr__math.html -

The returned value is in the range [-pi/2, pi/2] radians. A domain error occurs for arguments not in the range [-1, +1].
Title: Re: Inverse trig functions
Post by: Jetfire on Apr 05, 2013, 09:54 pm
Ok cool

Rewrote my arcsin() as asin and that compiled fine.

Including the conversion formula for radians to degrees didn't work so well.

The value pi is apparently not included in the package.

Should I just use "3.14159265358979323846" or is there some other way?

Thanks
Title: Re: Inverse trig functions
Post by: Jsut210 on Apr 05, 2013, 11:16 pm
The value of Pi isn't included with math.h.  You should just do something like:
Code: [Select]
`#define PI 3.14.....`
Then you can just use the "PI" definition where needed.
Title: Re: Inverse trig functions
Post by: WizenedEE on Apr 06, 2013, 02:30 am

The value of Pi isn't included with math.h.  You should just do something like:
Code: [Select]
`#define PI 3.14.....`
Then you can just use the "PI" definition where needed.

Arduino.h already defines PI
Title: Re: Inverse trig functions
Post by: Jsut210 on Apr 06, 2013, 02:34 am

The value of Pi isn't included with math.h.  You should just do something like:
Code: [Select]
`#define PI 3.14.....`
Then you can just use the "PI" definition where needed.

Arduino.h already defines PI

Even Better
Title: Re: Inverse trig functions
Post by: robtillaart on Apr 06, 2013, 01:06 pm
math.h does define: - http://www.nongnu.org/avr-libc/user-manual/group__avr__math.html -

#define    M_PI   3.14159265358979323846   /* pi */
#define    M_PI_2   1.57079632679489661923   /* pi/2 */
#define    M_PI_4   0.78539816339744830962   /* pi/4 */
#define    M_1_PI   0.31830988618379067154   /* 1/pi */
#define    M_2_PI   0.63661977236758134308   /* 2/pi */
#define    M_2_SQRTPI   1.12837916709551257390   /* 2/sqrt(pi) */

unfortunately math.h does not define 180/PI and PI/180  for radians <> degrees conversion
(windows calc)
#define     M_180_PI  57,295779513082320876798154814105   /*180/pi */
#define     M_PI_180  0,01745329251994329576923690768489    /* pi/180 */

// the arduino does only support about 7 digits of float precision so the above numbers are overkill  (unless the arbitrary precision lib is used )
Title: Re: Inverse trig functions
Post by: Jetfire on Apr 06, 2013, 11:23 pm

The value of Pi isn't included with math.h.  You should just do something like:
Code: [Select]
`#define PI 3.14.....`
Then you can just use the "PI" definition where needed.

Arduino.h already defines PI

OK

I changed pi to PI and it compiled OK

I'm waiting for hardware to test it out.

Anyone know where I can get 20-25 servos for under \$100?
Title: Re: Inverse trig functions
Post by: PaulS on Apr 07, 2013, 04:29 pm
Quote
Anyone know where I can get 20-25 servos for under \$100?

20 minus 25 is -5. You could send me 5 servos and \$100, and you'd have -5 servos for \$100.
Title: Re: Inverse trig functions
Post by: Jsut210 on Apr 07, 2013, 04:31 pm
These are about the cheapest servos you can get:

http://www.ebay.com/itm/Micro-9g-Mini-RC-Servo-for-Trex-450-Futaba-Hitec-HS-55-Align-GWS-JR-Walkera-Heli-/140922521530?pt=LH_DefaultDomain_0&hash=item20cfa307ba

Yep, straight from china.  Keep in mind that you get what you pay for.