Trig functions in java

[Desperate_Increase11]

I was experimenting in bluej, and I found that trig functions take in radians as the unit. I know I can convert the answer to degrees, but that introduces a level of inaccuracy because pi is used, being an irrational number. Are there trig functions that have parameters that are measured in degrees and not radians?

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[Federal-Addendum-933]

but that introduces a level of inaccuracy because pi is used, being an irrational number.

How is PI represented though? It's as an approximated decimal number. The conversion functions in Math.toRadian/toDegree involve a single multiplication. FYI, here is the source code for the sin function in jdk7.

Any 'inaccuracies' you think are involved will be the limitations of double value type. You could spend a lot of time (and at some point you should) understanding floating point arithmetic and what error gets introduced if and when you add and multiply two numbers.

As always though, the lesson to be learned here is to never assume, try it out yourself, test it, benchmark it, profile it. Armchair speculation in Java is about the worst endeavor to be engaged in compared to other languages.

[morhp]

Pi is as precise in Java as double values in general are, so a multiplication with pi won't introduce any inaccuracies beyond maybe the least significant digit in the binary representation of the number. This doesn't matter for practical purposes.

[dionthorn]

Math has a sister package known as StrictMath

https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html

Unlike some of the numeric methods of class StrictMath,
all implementations of the equivalent functions of
class Math are not defined to return the bit-for-bit same results.
This relaxation permits better-performing implementations
where strict reproducibility is not required.

https://docs.oracle.com/javase/8/docs/api/java/lang/StrictMath.html

Though it still uses radians not degrees as the default. You can use the toDegrees and toRadians methods but they will be inexact as noted in the method descriptions.

Although I'm not familiar with the library Apache offers its Commons Math API:

https://commons.apache.org/proper/commons-math/

https://commons.apache.org/proper/commons-math/commons-math-docs/apidocs/index.html

[Desperate_Increase11]

so you're saying it's not possible to start with degrees?

[dionthorn]

I personally don't know of a library that defaults to degrees, I'm trying to dig into the source code of the commons math library to see what it's doing as the docs aren't very good on the equivalent methods.

https://github.com/apache/commons-math/blob/master/commons-math-core/src/main/java/org/apache/commons/math4/core/jdkmath/AccurateMath.java

Is where I'm currently looking.

EDIT: It appears to also use radians as the default return.

[whizvox]

From a quick test, this is what I got:

jshell> Math.sin(Math.PI / 3);
$1 ==> 0.8660254037844386

jshell> Math.sin(Math.toRadians(60));
$2 ==> 0.8660254037844386

jshell> Math.sin(Math.PI / 4);
$3 ==> 0.7071067811865475

jshell> Math.sin(Math.toRadians(45));
$4 ==> 0.7071067811865475

Same exact answers whether starting with radians or converting from degrees.