Why does the result of Math.pow(-0.9, 0.8) in Java produce NaN?

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When the result of the operations involving Double or Float data types in Java produces some unpredicatable output, it is designated by NaN (Not a Number).

Why does the statement that uses Math.pow() produce NaN?

Java

System.out.println(Math.pow(-0.9, 0.8));

Of course, it may be easy for you, I can't figure it out, please.

Posted 24-Oct-12 5:39am

Lion 2012

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4 solutions

Solution 3

Have you ever heard of complex number? In not complex number, have you ever heard that, in real numbers, square root of negative number cannot be found; in other words, the equation x² = −1 has no solutions in read numbers?! And, of course, the same stands for 0.8 and −0.9.

This is something like middle school… and such school should be a prerequisite for starting with computing.

And NaN means "not a number", important object reserved to IEEE 754 floating number representation to represent the concept of invalid number. Please see:
http://en.wikipedia.org/wiki/IEEE_754[^].

(Sigh…)

—SA

Posted 24-Oct-12 11:23am

Sergey Alexandrovich Kryukov

Updated 24-Oct-12 11:32am

v5

Solution 1

I'm guessing it's because the result is complex, according to WolframAlpha[^], and the float/double type isn't able to represent it.

Posted 24-Oct-12 5:51am

lewax00

Solution 4

For understanding it you should know that:

(Math) The result of power operation might be a complex number (when base is negative and exponent is not integer).
(Computing) pow returns a double. Such datatype cannot represent a complex number (technically it 'approximates' a real number).

Reading the pow method documentation[^] would help too.

Posted 24-Oct-12 11:46am

CPallini

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Sandeep Mewara · Accepted Answer · 2012-10-24T05:51:00

That's how it works. Here, read at the details: Java.lang.Math.pow() Method[^]

If the first argument is finite and less than zero:
- if the second argument is a finite even integer, the result is equal to the result of raising the absolute value of the first argument to the power of the second argument
- if the second argument is a finite odd integer, the result is equal to the negative of the result of raising the absolute value of the first argument to the power of the second argument
- if the second argument is finite and not an integer, then the result is NaN.