Hello,
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.
---
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 ?
Best regards,
Yannick TANGUY
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