Why is it that when I have X(long) / (Y*Y*Y)(long) I get Error: Divide by Zero?

In my example X is already long and Y is a long also. I am not casting at then.

I really just want to divide by a number that is cubed. (using native libraries)

These numbers are extremely large. If I convert them to floats and do it, its value is Infinite...

System.out.println(formatter.format("%20d", (X/(Y*Y*Y))));

Y is an extremely large number, it is not 0. X is a measurement of time in milliseconds.

I will post the exact code in a short while if this question doesn't get closed... I don't have access to it right this minute.

Context: I am dealing with a big notation calculation for O(n^3).

Error: "Exception in thread "main" java.lang.ArithmeticException: / by zero"

Answers:

Assuming you didn't really mean the quotes, the likely reason is that Y * Y * Y is greater than 2 ^ 31. It's overflowing, with a lower part of 0. I believe this would only happen if Y is a multiple开发者_C百科 of 2^11 (2048) - but I'm not certain*

-This is the case for me, Y is a multiple of 2048, hopefully this helps with trying to find a solution.

    // Algorithm 3
    for( int n = 524288; n <= 5000000; n *= 2 ){
        int alg = 3;
        long timing;
        maxSum = maxSubSum3( a );
        timing = getTimingInfo( n, alg );
        System.out.println(fmt.format("%20s %20d %20d %20d %20d %20s%n", "Alg. 3", n, timing, timing, timing/(n*n), "time/(n*log(n))"));
    }

Assuming you didn't really mean the quotes, the likely reason is that Y * Y * Y is greater than 2 ^ 31. It's overflowing, with a lower part of 0.

I believe this would only happen if Y is a multiple of 2^11 (2048) - but I'm not certain.

It can be avoided by making sure that the computation of Y^3 is done using some datatype that can hold it. If it's less than 2 million, you can use a long instead. If not, you'll have to either use a double or a BigInteger. Given that your other value is in milliseconds, I'd guess that floating point would be fine. So you'd end up with:

System.out.println(formatter.format("%20d", (int)(X/((double)Y*Y*Y))));

You may want to use floating point for the output as well - I assumed not.

Surely you don't mean to pass "(X/(Y*Y*Y))" as a string literal? that's a string containing your express, and not compilable Java code that expresses a computation that Java will perform. So that's problem #1: remove those quotes.

Second, the formatter has nothing to do with dividing numbers, so that is not relevant nor your problem.

Third, casting has nothing to do with this. Your problem is exactly what it says: you're dividing by zero. I assume you don't want to do that. So, Y must be 0.

Fourth, nothing here uses native libraries. It's all Java. Right, that's what you mean?

You may want to use BigInteger to perform math on very large values that overflow a long. But, that will not make division by zero somehow not be division by zero.

Perhaps you should try, either with long or float conversions:

( ( X / Y ) / Y ) / Y

If Y is a high enough power of 2 (2^22 or more), then Y^3 will be a higher than 2^64 power of 2. And long uses 64 bits in Java, isn't that correct?