单选题：A tri-diagonal matrix is a square matrix with nonzero elements o
A tri-diagonal matrix is a square matrix with nonzero elements only on the diagonal and slots horizontally or vertically adjacent the diagonal, as shown in the figure.
Given a tri-diagonal matrix (三对角矩阵) $$M$$ of order 100. Compress the matrix by storing its tri-diagonal entries $$m_{i,j}$$ ($$1\le i\le 100$$，$$1\le j\le 100$$) row by row into a one dimensional array $$N$$ with indices starting from 0. Then the index of $$m_{30,30}$$ in $$N$$ is:
@[B](2)
A. 86
B. 87
C. 88
D. 89
A.86
B.87
C.88
D.89
答案：B
Given a tri-diagonal matrix (三对角矩阵) $$M$$ of order 100. Compress the matrix by storing its tri-diagonal entries $$m_{i,j}$$ ($$1\le i\le 100$$，$$1\le j\le 100$$) row by row into a one dimensional array $$N$$ with indices starting from 0. Then the index of $$m_{30,30}$$ in $$N$$ is:
@[B](2)
A. 86
B. 87
C. 88
D. 89
A.86
B.87
C.88
D.89
答案：B