# What is Math.atan() returning?

dave taubler

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Posts: 132

posted 12 years ago

I am trying to simply find the angle between two points. I'm trying to get the arc tangent to derive the angle, but Math.atan() doesn not seem to return an angle of any sort. I've reduce my code to a simple example:

double distanceAngle = Math.atan(0.2455);

System.out.println("angle = " + distanceAngle);

that prints:

angle = 0.24073890523107128

If I go to any calculator and get the arc tangent of 0.2455, I get 13.79 degrees, which is the angle I am looking for. So......... does anyone know what Math.atan() is returning?

double distanceAngle = Math.atan(0.2455);

System.out.println("angle = " + distanceAngle);

that prints:

angle = 0.24073890523107128

If I go to any calculator and get the arc tangent of 0.2455, I get 13.79 degrees, which is the angle I am looking for. So......... does anyone know what Math.atan() is returning?

Dave Taubler<br />Specializing in <a href="http://taubler.com/articles/" target="_blank" rel="nofollow">Java and Web Development</a>

Jim Yingst

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Surasak Leenapongpanit

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Posts: 341

posted 12 years ago

java doc 1.4.2

atan

public static double atan(double a)Returns the arc tangent of an angle, in the range of -pi/2 through pi/2. Special cases:

If the argument is NaN, then the result is NaN.

If the argument is zero, then the result is a zero with the same sign as the argument.

A result must be within 1 ulp of the correctly rounded result. Results must be semi-monotonic.

Parameters:

a - the value whose arc tangent is to be returned.

Returns:

the arc tangent of the argument.

posted 12 years ago

Here's the link you need to the API. I'd bookmark this site, and refer to it frequently. It will answer many of the question like this you may have, and probably be faster than posting here. But don't hesitate to ask here when you can't find the answer!!!

:-)

:-)

There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors

dave taubler

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Posts: 132

posted 12 years ago
Dave Taubler<br />Specializing in <a href="http://taubler.com/articles/" target="_blank" rel="nofollow">Java and Web Development</a>

Hi,

Thanks to everyone who replied, I do appreciate it. The reason I wrote is that I *did* go through the JavaDocs, and they were no help (even Surasak Leenapongpanit's reposting of the atan() API says nothing about radians); I Googled for about half an hour as well, to no avail. Believe me, I do all the research I reasonably can before posting!

Thanks to everyone who replied, I do appreciate it. The reason I wrote is that I *did* go through the JavaDocs, and they were no help (even Surasak Leenapongpanit's reposting of the atan() API says nothing about radians); I Googled for about half an hour as well, to no avail. Believe me, I do all the research I reasonably can before posting!

Peter Chase

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Posts: 1970

posted 12 years ago

In the version of the API JavaDocs that I have (1.4.2, I think), it does mention radians in many of the math functions, but not in atan(). It does give a clue by saying that the result of atan() will be between plus and minus pi/2, though, which is a hint at radians.

I reckon the person who wrote the docs was a mathematician or engineer for whom radians would be the "obvious" representation. But degrees are still the most common representation of angles, for most people.

I reckon the person who wrote the docs was a mathematician or engineer for whom radians would be the "obvious" representation. But degrees are still the most common representation of angles, for most people.

Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.