INDEX matrix function
INDEX(A,r,c) Returns the element of matrix A located on row r and column c.
If row number r is zero, then a single column n × 1 matrix is returned with the data of column c.
If column number c is zero, then a single row 1 × n matrix is returned with the data of row r.
Matrix Algebra Useful for Statistics
Shayle R. Searle, Andre I. Khuri
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