Understanding Convex Functions Quiz
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Questions and Answers

Which of the following is a convex function?

  • Logarithm function: $log(x)$, for any $x > 0$
  • Powers of absolute value: $|x|^p$, for $p \geq 1$
  • Negative part function: $min\{0, x\}$
  • Exponential function: $e^x$, for any $x \in R$ (correct)

Which function is a concave function?

  • Sum of squares function: $\|x\|^2 = x_1^2 + \cdots + x_n^2$
  • Entropy function: $-x \log x$ for $x > 0$ (correct)
  • Affine function: $ax + b$, for any $a, b \in R$
  • Powers function: $x^\alpha$, for $0 \leq \alpha \leq 1$

Which of the following is an example of a convex function on $R^{m \times n}$?

  • Sum of squares: $\|x\|^2 = x_1^2 + \cdots + x_n^2$
  • Softmax or log-sum-exp function: $log(exp(x_1) + \cdots + exp(x_n))$
  • General affine function: $f(X) = tr(A^TX) + b$ (correct)
  • Max function: $max(x) = max\{x_1, x_2, \ldots, x_n\}$

Which of the following functions is strictly convex?

<p>Exponential function: $e^x$, for any $x \in R$ (D)</p> Signup and view all the answers

Which of the following functions is a concave function?

<p>Sum of squares: $|x|^2 = x_1^2 + \cdots + x_n^2$ (A)</p> Signup and view all the answers

Which of the following best defines a convex function?

<p>A function where the domain is convex and satisfies $f( \theta x + (1 - \theta)y) \leq \theta f(x) + (1 - \theta)f(y)$ (D)</p> Signup and view all the answers

Which of the following is an example of a concave function on $R^{n}$?

<p>Logarithm: $log(x)$ (A)</p> Signup and view all the answers

Which function is a strictly convex function?

<p>Exponential: $e^x$ (D)</p> Signup and view all the answers

Which of the following functions is an example of a convex function on $R^{m\times n}$?

<p>Sum of squares: $|x|^2 = x_1^2 + x_2^2 + ... + x_n^2$ (B)</p> Signup and view all the answers

Which of the following is NOT an example of a convex function on $R^{n}$?

<p>Powers: $x^\alpha$ for $\alpha geq 1$ or $\alpha leq 0$ (C)</p> Signup and view all the answers

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