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1. Are instances of org.apache.commons.math.stat.descriptive.DescriptiveStatisticsImpl thread-safe?
No, they are not. By design, we chose not to introduce thread semantics into the classes. This allows the library to be used in environments where thread management by the application is to be avoided. The same is true of many other classes in commons-math, including the solvers in the analysis packageVersion 2.0 includes synchronized versions of several classes, including a SynchronizedDescriptiveStatistics class.
2. Can code derived from "Numerical Recipes" routines be included in commons-math?
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