请用中文帮我翻译并回答以下问题Which of the following statements about $k$-Nearest Neighbor ($k$-NN) are true in a classification setting, and for all $k$? Select all that apply. 1. The decision boundary of the k-NN classifier is linear. 2. The training error of a 1-NN will always be lower than or equal to that of 5-NN. 3. The test error of a 1-NN will always be lower than that of a 5-NN. 4. The time needed to classify a test example with the k-NN classifier grows with the size of the training set. 5. None of the above.

以下哪些关于$k$-最近邻($k$-NN)在分类问题中的说法是正确的，并且对于所有的$k$都适用？请选择所有正确的说法。1. $k$-NN分类器的决策边界是线性的。2. 1-NN的训练误差总是低于或等于5-NN的训练误差。3. 1-NN的测试误差总是低于5-NN的测试误差。4. 使用$k$-NN分类器对一个测试样本进行分类所需的时间会随着训练集的大小增加而增加。5. 以上说法均不正确。

正确答案是2和4。2是正确的，因为1-NN是完全依赖训练数据的，因此它的训练误差应该是最小的。4是正确的，因为使用$k$-NN分类器对每个测试样本进行分类时，都需要计算与所有训练样本之间的距离，因此随着训练集的大小增加，所需的时间也会增加。1、3、5都是不正确的。

相关问题

Which of the following statements is preferred to create a string "Welcome to Java"?

The most preferred way to create a string "Welcome to Java" is:

String str = "Welcome to Java";

This creates a string literal and assigns it to the variable `str`. String literals are preferred over creating strings using the `new` operator because they are more efficient and use less memory. When a string literal is encountered, the Java compiler creates a single instance of the string in the string pool and all references to the same string literal point to this instance.

Therefore, using a string literal is the most preferred way to create a string in Java.

Q21: Which of the following is a valid user-defined output stream manipulator header? a. ostream& tab( ostream& output ) b. ostream tab( ostream output ) c. istream& tab( istream output ) d. void tab( ostream& output ) Q22: What will be output by the following statement? cout << showpoint << setprecision(4) << 11.0 << endl; a. 11 b. 11.0 c. 11.00 d. 11.000 Q23: Which of the following stream manipulators causes an outputted number’s sign to be left justified, its magnitude to be right justified and the center space to be filled with fill characters? a. left b. right c. internal d. showpos Q24: Which of the following statements restores the default fill character? a. cout.defaultFill(); b. cout.fill(); c. cout.fill( 0 ); d. cout.fill( ' ' ); Q25: When the showbase flag is set: a. The base of a number precedes it in brackets. b. Decimal numbers are not output any differently. c. "oct" or "hex" will be displayed in the output stream. d. Octal numbers can appear in one of two ways. Q26: What will be output by the following statements? double x = .0012345; cout << fixed << x << endl; cout << scientific << x << endl; a. 1.234500e-003 0.001235 b. 1.23450e-003 0.00123450 c. .001235 1.234500e-003 d. 0.00123450 1.23450e-003 Q27: Which of the following outputs does not guarantee that the uppercase flag has been set? a. All hexadecimal numbers appear in the form 0X87. b. All numbers written in scientific notation appear the form 6.45E+010. c. All text outputs appear in the form SAMPLE OUTPUT. d. All hexadecimal numbers appear in the form AF6. Q28: Which of the following is not true about bool values and how they're output with the output stream? a. The old style of representing true/false values used -1 to indicate false and 1 to indicate true. b. A bool value outputs as 0 or 1 by default. c. Stream manipulator boolalpha sets the output stream to display bool values as the strings "true" and "false". d. Both boolalpha and noboolalpha are “sticky” settings.

A21: a. ostream& tab( ostream& output ) is a valid user-defined output stream manipulator header.

A22: c. 11.00 will be output by the statement.

A23: c. internal is the stream manipulator that causes an outputted number’s sign to be left justified, its magnitude to be right justified and the center space to be filled with fill characters.

A24: d. cout.fill(' ') restores the default fill character, which is a space.

A25: c. "oct" or "hex" will be displayed in the output stream when the showbase flag is set.

A26: b. 1.23450e-003 and 1.23450e-003 will be output by the statements.

A27: d. All hexadecimal numbers appearing in the form AF6 does not guarantee that the uppercase flag has been set.

A28: a. The old style of representing true/false values used -1 to indicate false and 1 to indicate true is not true. False is represented by 0 and true is represented by any non-zero value.