# 코쉬 행렬과 행렬식

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## 개요

• 행렬 $$A=({\frac{1}{x_i-y_j}})_{1\le i,j\le n}$$를 크기 n인 코쉬 행렬이라 함
• 행렬식

$\det \left(\frac{1}{x _i-y _j}\right) _{1\le i,j \le n}=(-1)^{\binom{n}{2}}\frac{\prod _{1\le i < j\le n} (x_j-x _i)(y _j-y _i)}{\prod _{i,j=1}^n (x _i-y _j)}$ $\det \left(\frac{1}{x _i+y _j}\right) _{1\le i,j \le n}=\frac{\prod _{1\le i < j\le n} (x_j-x _i)(y _j-y _i)}{\prod _{i,j=1}^n (x _i+y _j)}$

## 예

### n=1인 경우

• $$\left( \begin{array}{c} \frac{1}{x_1-y_1} \end{array} \right)$$

### n=2인 경우

• 코쉬 행렬

$\left( \begin{array}{cc} \frac{1}{x_1-y_1} & \frac{1}{x_1-y_2} \\ \frac{1}{x_2-y_1} & \frac{1}{x_2-y_2} \end{array} \right)$

• 행렬식

$\frac{\left(x_1-x_2\right) \left(y_1-y_2\right)}{\left(x_1-y_1\right) \left(y_1-x_2\right) \left(x_1-y_2\right) \left(x_2-y_2\right)}$

### n=3인 경우

• 코쉬 행렬은

$\left( \begin{array}{ccc} \frac{1}{x_1-y_1} & \frac{1}{x_1-y_2} & \frac{1}{x_1-y_3} \\ \frac{1}{x_2-y_1} & \frac{1}{x_2-y_2} & \frac{1}{x_2-y_3} \\ \frac{1}{x_3-y_1} & \frac{1}{x_3-y_2} & \frac{1}{x_3-y_3} \end{array} \right)$

• 행렬식은

$-\frac{\left(-x_1+x_2\right) \left(-x_1+x_3\right) \left(-x_2+x_3\right) \left(y_1-y_2\right) \left(y_1-y_3\right) \left(y_2-y_3\right)}{\left(x_3-y_1\right) \left(-x_1+y_1\right) \left(-x_2+y_1\right) \left(x_2-y_2\right) \left(x_3-y_2\right) \left(-x_1+y_2\right) \left(x_1-y_3\right) \left(x_2-y_3\right) \left(x_3-y_3\right)}$

### n=4인 경우

• 코쉬 행렬은

$\left( \begin{array}{cccc} \frac{1}{x_1-y_1} & \frac{1}{x_1-y_2} & \frac{1}{x_1-y_3} & \frac{1}{x_1-y_4} \\ \frac{1}{x_2-y_1} & \frac{1}{x_2-y_2} & \frac{1}{x_2-y_3} & \frac{1}{x_2-y_4} \\ \frac{1}{x_3-y_1} & \frac{1}{x_3-y_2} & \frac{1}{x_3-y_3} & \frac{1}{x_3-y_4} \\ \frac{1}{x_4-y_1} & \frac{1}{x_4-y_2} & \frac{1}{x_4-y_3} & \frac{1}{x_4-y_4} \end{array} \right)$

## 관련논문

• Ishikawa, Masao, Soichi Okada, Hiroyuki Tagawa, and Jiang Zeng. “Generalizations of Cauchy’s Determinant and Schur’s Pfaffian.” Advances in Applied Mathematics 36, no. 3 (2006): 251–87. doi:10.1016/j.aam.2005.07.001.
• Chen, William Y. C., Christian Krattenthaler, and Arthur L. B. Yang. “The Flagged Cauchy Determinant.” Graphs and Combinatorics 21, no. 1 (2005): 51–62. doi:10.1007/s00373-004-0593-9.

## 메타데이터

### Spacy 패턴 목록

• [{'LOWER': 'cauchy'}, {'LEMMA': 'matrix'}]