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<用Doolittle分解求方阵的逆>

  设A=LR,L为单位下三角阵,R为上三角阵,则A-1 =R-1 L-1,分别求出R-1和L-1,相乘即可得A-1。

  (使用说明)
输入参数:
N   方阵A(N,N)的阶数。
A(N,N)     N阶方阵,按行存放。

输出参数:
W   标志,W=0说明A非奇异,W=1表示A奇异,不存放A的逆。
D(N,N)     存放A的逆的元素。

中间工作单元:
C(N,N)   N阶方阵
                      
               (下面有VB的程序,麻烦帮我改改成PASCAL好吗)

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*             用Doolittle 分解求方阵的逆           *
30  '******************************************************
50  Dim A(N, N), C(N, N), D(N, N)
60  Print Tan(3); "EG:"; Tab(8); "THE MATRIX A": Print
70  For I = 1 To N: For J = 1 To N
80  READ A(I, J): Print USING; "####.#"; A(I, J);
90  Next J: Print: Next I
100 Print: GoSub 300
110  Print Tab(5); "W="; W: Print
120  If W = 1 Then GoTo 190
130  Print Tab(15); "THE CONVERSE MATRIX OF A": Print
140 For I = 1 To N: For J = 1 To N
150 Print USING; "####.#####"; D(I, J);: Print " ";
160 Next J: Print: Next I
170 Data 1, 2, 3, 4, 1, 4, 9, 16, 1, 8, 27, 64, 1, 16, 81, 256
180 Data
190 End
300 '子程序'
310 '分解'
320 If A(1, 1) = 0 Then GoTo 890
330 For I = 2 To N: A(I, 1) = A(I, 1) / A(1, 1)
340 Next I
350 P = 0
360 For K = 2 To N: For J = K To N
370   For R = 1 To K - 1
380   P = P + A(K, R) * A(R, J)
390   Next R
400   A(K, J) = A(K, J) - P: P = 0
410  Next J
420  P = 0
430  For I = K + 1 To N: For R = 1 To K - 1
440  P = P + A(I, R) * A(R, K)
450  Next R
460 If A(K, K) = 0 Then GoTo 890
470  A(I, K) = (A(I, K) - P) / A(K, K): P = 0
480  Next I
490 Next K
500 For I = 1 To N: For J = 1 To I
510 If J = I Then C(I, I) = 1
520 If J <> I Then C(I, J) = A(I, J)
530 If J <> I Then A(I, J) = 0
540 Next J: Next I
550 '上三角求逆'
560 For K = N To 1 Step -1
570 If A(K, K) = 0 Then GoTo 890
580 A(K, K) = 1 / A(K, K)
590   For I = K - 1 To 1 Step -1
600   P = 0
610     For J = I + 1 To K
620     P = P - A(I, J) * A(J, K)
630     Next J
640     A(I, K) = P / A(I, I)
650   Next I
660 Next K
670 '下三角求逆'
680 For K = 1 To N: For I = K + 1 To N
690 P = 0
700     For J = I - 1 To K Step -1
710     P = P - C(I, J) * C(J, K)
720     Next J
730     C(I, K) = P / C(I, I)
740 Next I: Next K
750 '求A的逆'
760 For I = 1 To N: For J = I + 1 To N
770 C(I, J) = 0
780 Next J: Next I
790 For J = 1 To N: For I = J + 1 To N
800 A(I, J) = 0
810 Next I: Next J
820 For I = 1 To N: For J = 1 To N
830 D(I, J) = 0
840   For K = 1 To N
850   D(I, J) = D(I, J) + A(I, K) * C(K, J)
860   Next K
870 Next J: Next I
880 W = 0: Return
890 W = 1: Return

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