}

  static class MeanAndVariance {
    private final double mean;
    private final double variance;

    MeanAndVariance(double mean, double variance) {
      this.mean = mean;
      this.variance = variance;
    }

    @Override
    public int hashCode() {
      return Double.hashCode(mean) * 31 + Double.hashCode(variance);
    }
  }

  enum VarianceAlgorithm {
    DO_NOT_COMPUTE {
      @Override

   * either the {@code x} or {@code y} data must have a non-zero population variance (i.e. {@code
   * xStats().populationVariance() > 0.0 || yStats().populationVariance() > 0.0}). The result is
   * guaranteed to be horizontal if there is variance in the {@code x} data but not the {@code y}
   * data, and vertical if there is variance in the {@code y} data but not the {@code x} data.
   *

                double variance = (maxTime - minTime) / avgTime;
                // JVM timing in concurrent scenarios is inherently variable
                // We verify implementation correctness rather than precise timing
                assertTrue(variance < 50.0,
                        String.format(

    return Math.sqrt(populationVariance());
  }

  /**
   * Returns the <a href="http://en.wikipedia.org/wiki/Variance#Sample_variance">unbiased sample
   * variance</a> of the values. If this dataset is a sample drawn from a population, this is an
   * unbiased estimator of the population variance of the population. The count must be greater than
   * one.
   *

    boolean longWait = NANOSECONDS.toSeconds(thread.timeSpentBlocked) >= 5;
    // Count how long it actually took to return; we'll accept any number between the expected delay
    // and the approximate actual delay, to be robust to variance in thread scheduling.
    char overWaitNanosFirstDigit =
        Long.toString(thread.timeSpentBlocked - MILLISECONDS.toNanos(longWait ? 5000 : 3000))
            .charAt(0);
    if (overWaitNanosFirstDigit < '4') {

    boolean longWait = NANOSECONDS.toSeconds(thread.timeSpentBlocked) >= 5;
    // Count how long it actually took to return; we'll accept any number between the expected delay
    // and the approximate actual delay, to be robust to variance in thread scheduling.
    char overWaitNanosFirstDigit =
        Long.toString(thread.timeSpentBlocked - MILLISECONDS.toNanos(longWait ? 5000 : 3000))
            .charAt(0);
    if (overWaitNanosFirstDigit < '4') {

### Bug Fixes and Other Changes

*   `tf.Variable`

    *   Changed resource variables to inherit from `tf.compat.v2.Variable` instead of `tf.compat.v1.Variable`. Some checks for `isinstance(v, tf compat.v1.Variable)` that previously returned True may now return False.

*   `tf.distribute`

The value of the variable `PATH` is a long string that is made of directories separated by a colon `:` on Linux and macOS, and by a semicolon `;` on Windows.

For example, the `PATH` environment variable could look like this:

//// tab | Linux, macOS

```plaintext
/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
```

    }

    /**
     * Returns the system environment variable value for the specified key.
     *
     * @param key the environment variable key
     * @return the environment variable value, or null if not found
     */
    public static String getEnv(String key) {
        return System.getenv(key);
    }

    /**
     * Returns the system environment variable value for the specified key, or the default value if not found.

        checkArgument(!variable.equalsType(type), "Type variable %s bound to itself", variable);
        builder.put(variable, type);
      }
      return new TypeTable(builder.buildOrThrow());
    }

    final Type resolve(TypeVariable<?> var) {
      TypeTable unguarded = this;
      TypeTable guarded =
          new TypeTable() {
            @Override