No atan() method in FRC version of java

Technical Java
1

I am trying to program a swerve drive, and I need to use atan(), but netbeans always says it doesn’t exist in my class. Yes I know there is getDirection() on the joystick, but I need to manipulate numbers after taking them from the joystick.

Thanks in advance

Alex

2

Alex:

Take a look in the com.sun.squawk.util.MathUtils package. There are implementations of many of the J2SE math functions, including atan() and atan2(), in there.

3

Team 20 had the same problem. We ended up writing a Talyor approximation and reflecting it about the axis to produce our own atan2 function.

4

What is the import line I need to use? I tried ‘import com.sun.squawk.util.MathUtils;’ and that did not work. I have yet to learn what Taylor series are in detail, so that would be a project for down the road.

5

Ok well I figured it out. I needed to call MathUtils.atan(). I wasn’t using MathUtils befroe. Thanks for the input though everybody.

6

What are you using the atan() function for?
If you are going to have negative numbers for the input, it may be better to use atan2(x,y).

7

Did you mean to say atan2(y,x)? Or does Java really reverse the order like Excel does. Say it ain’t so.

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8

Sorry, that was a typo.
Here is the actual function header:


double atan2(double y, double x) ;
9

I am using it to calcluate the desired angle of a wheel in a swerve configuration. I calculate the x and y components of the vector representing each wheel. Getting the magnitude (speed) is easy, but without atan, the angle was going to be a challenge.

10

Taylor expansion is not the best tool to use for this purpose.

See the discussion about ATAN2 nonlinear model fitting here:

http://www.chiefdelphi.com/media/papers/2390

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11

I spent the summer porting a fixed point math library to Arm’s Thumb2 assembly, and learned a lot when I hit the arc-trig functions. At the high school level, suffice it to say that these functions are very-not-polynomials and therefore hate Taylor series expansions. At the college level, suffice it to say that if I ever teach numerical approximations the final exam will be to approximate arcsine.