Java double subtraction oddity (not the usual rounding discrepancy)
I've been going through a java tutorial, and ran across some strangeness in this small example...
Code:
class SqrRoot {
public static void main(String args[]) {
double num,sroot,rerr,resquare;
for(num = 1.0; num < 100.0; num++) {
sroot = Math.sqrt(num);
System.out.println("Square root of " + num + " is " + sroot);
// compute rounding error
resquare = (sroot * sroot);
rerr = num - resquare;
System.out.println("Rounding error: num + " - " + resquare + " = " + rerr);
System.out.println();
}
}
}
The return is strange -- when I saw the results, I written a small program that subtracted a number of literal floating point numbers, all with the normal binary to decimal oddness (1.002 - 1.001 = .000999999997); yet when I run the above code, I get what's below:
Code:
Square root of 1.0 is 1.0
1.0 - 1.0 = 0.0
Square root of 2.0 is 1.4142135623730951
2.0 - 2.0000000000000004 = -4.440892098500626E-16
Square root of 3.0 is 1.7320508075688772
3.0 - 2.9999999999999996 = 4.440892098500626E-16
....
I'm not sure if it's something I'm doing wrong or what is causing it. I've searched all over and all I've found is people asking about the hardware limitations of floating point arithmetic. Any help would be greatly appreciated.
-----Post Update-----
After seeing it posted here I just realized I wasn't taking into account the scientific notation... Boy to I feel dumb now
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Discussion started by: beomagi
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LEARN ABOUT SUNOS
frexp
frexp(3M) Mathematical Library Functions frexp(3M)NAME
frexp, frexpf, frexpl - extract mantissa and exponent from a floating-point number
SYNOPSIS
cc [ flag... ] file... -lm [ library... ]
#include <math.h>
double frexp(double num, int *exp);
float frexpf(float num, int *exp);
long double frexpl(long double num, int *exp);
DESCRIPTION
These functions break a floating-point number into a normalized fraction and an integral power of 2. They store the integer exponent in the
int object pointed to by exp.
RETURN VALUES
For finite arguments, these functions return the value x, such that x is a double with magnitude in the interval [1/2, 1) or 0, and num
equals x times 2 raised to the power *exp.
If num is NaN, NaN is returned and the value of *exp is unspecified.
If num is +- 0, +- 0 is returned and the value of *exp is 0.
If num is +-Inf, num is returned and the value of *exp is unspecified.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |MT-Safe |
+-----------------------------+-----------------------------+
SEE ALSO isnan(3M), ldexp(3M), modf(3M), attributes(5), standards(5)SunOS 5.10 16 Aug 2004 frexp(3M)
06-13-2009
