Le 19/09/2012 15:02, Tanguy Yannick a écrit : > Hello, Hi Yannick,
> > This message is about some methods in Precision class, and follows a > discussion about MATH-863 > (https://issues.apache.org/jira/browse/MATH-863). > > Recently, we slightly modified our Precision class, by adding a > specific epsilon value to compute a relative deviation and also some > methods. --- /** Epsilon used for doubles relative comparison */ > public static final double DOUBLE_COMPARISON_EPSILON = 1.0e-14; --- > > This value is quite useful to compare two values. It's > approximatively 100 times larger than the previous EPSILON value > (1e-16, the difference between 1. and the next closest value). > > We also added static methods, to compute a relative difference : if > x1 and x2 are not equal (according to the equals(x1,x2, "1 ulp") > function), then we compute a relative deviation > ("abs(x1-x2)/max(abs(x1),abs(x2))" and see if it's lower than an > epsilon value. The comparison should probably rather be: abs(x1-x2) <= eps * max(abs(x1),abs(x2) The reason for that is that with your implementation when both x1 and x2 are 0 (either +0 or -0), then the result would be false, despite the numbers are equal. The division 0/0 leads to a NaN and all comparisons involving NaN return false. > > --- public static boolean equalsWithRelativeTolerance(final double x, > final double y) -> uses the DOUBLE_COMPARISON_EPSILON public static > boolean equalsWithRelativeTolerance(final double x, final double y, > final double eps) --- > > These kind of methods are used in some of our tools (space dynamic > libraries) to assert equality between values, when we don't know the > order of magnitude. > > Do you think it's useful for Commons Math users ? Shall I open a > ticket on JIRA and contribute the corresponding code source ? Yes, along with test cases, including special cases (+/-0, +/-infinity, NaNs, +/-Double.MAX_VALUE, +/-Double.MIN_VALUE ...) best regards, Luc > > Best regards, > > Yannick TANGUY > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org > For additional commands, e-mail: dev-h...@commons.apache.org > > --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
