Python計算——高斯消元法解線性方程組
阿新 • • 發佈:2019-02-15
#!/usr/bin/env python # coding=gb2312 # 以上的資訊隨自己的需要改動吧 def print_matrix( info, m ): # 輸出矩陣 i = 0; j = 0; l = len(m) print info for i in range( 0, len( m ) ): for j in range( 0, len( m[i] ) ): if( j == l ): print ' |', print '%6.4f' % m[i][j], print print def swap( a, b ): t = a; a = b; b = t def solve( ma, b, n ): global m; m = ma # 這裡主要是方便最後矩陣的顯示 global s; i = 0; j = 0; row_pos = 0; col_pos = 0; ik = 0; jk = 0 mik = 0.0; temp = 0.0 n = len( m ) # row_pos 變數標記行迴圈, col_pos 變數標記列迴圈 print_matrix( "一開始 de 矩陣", m ) while( ( row_pos < n ) and( col_pos < n ) ): print "位置:row_pos = %d, col_pos = %d" % (row_pos, col_pos) # 選主元 mik = - 1 for i in range( row_pos, n ): if( abs( m[i][col_pos] ) > mik ): mik = abs( m[i][col_pos] ) ik = i if( mik == 0.0 ): col_pos = col_pos + 1 continue print_matrix( "選主元", m ) # 交換兩行 if( ik != row_pos ): for j in range( col_pos, n ): swap( m[row_pos][j], m[ik][j] ) swap( m[row_pos][n], m[ik][n] ); # 區域之外? print_matrix( "交換兩行", m ) try: # 消元 m[row_pos][n] /= m[row_pos][col_pos] except ZeroDivisionError: # 除零異常 一般在無解或無窮多解的情況下出現…… return 0; j = n - 1 while( j >= col_pos ): m[row_pos][j] /= m[row_pos][col_pos] j = j - 1 for i in range( 0, n ): if( i == row_pos ): continue m[i][n] -= m[row_pos][n] * m[i][col_pos] j = n - 1 while( j >= col_pos ): m[i][j] -= m[row_pos][j] * m[i][col_pos] j = j - 1 print_matrix( "消元", m ) row_pos = row_pos + 1; col_pos = col_pos + 1 for i in range( row_pos, n ): if( abs( m[i][n] ) == 0.0 ): return 0 return 1 if __name__ == '__main__': matrix = [[2.0, 0.0, - 2.0, 0.0], [0.0, 2.0, - 1.0, 0.0], [0.0, 1.0, 0.0, 10.0]] i = 0; j = 0; n = 0 # 輸出方程組 print_matrix( "一開始的矩陣", matrix ) # 求解方程組, 並輸出方程組的可解資訊 ret = solve( matrix, 0, 0 ) if( ret!= 0 ): print "方程組有解\n" else: print "方 程組無唯一解或無解\n" # 輸出方程組及其解 print_matrix( "方程組及其解", matrix ) for i in range( 0, len( m ) ): print "x[%d] = %6.4f" % (i, m[i][len( m )])
>>> ================================ RESTART ================================ >>> 一開始的矩陣 2.0000 0.0000 -2.0000 | 0.0000 0.0000 2.0000 -1.0000 | 0.0000 0.0000 1.0000 0.0000 | 10.0000 一開始 de 矩陣 2.0000 0.0000 -2.0000 | 0.0000 0.0000 2.0000 -1.0000 | 0.0000 0.0000 1.0000 0.0000 | 10.0000 位置:row_pos = 0, col_pos = 0 選主元 2.0000 0.0000 -2.0000 | 0.0000 0.0000 2.0000 -1.0000 | 0.0000 0.0000 1.0000 0.0000 | 10.0000 交換兩行 2.0000 0.0000 -2.0000 | 0.0000 0.0000 2.0000 -1.0000 | 0.0000 0.0000 1.0000 0.0000 | 10.0000 消元 1.0000 0.0000 -1.0000 | 0.0000 0.0000 2.0000 -1.0000 | 0.0000 0.0000 1.0000 0.0000 | 10.0000 位置:row_pos = 1, col_pos = 1 選主元 1.0000 0.0000 -1.0000 | 0.0000 0.0000 2.0000 -1.0000 | 0.0000 0.0000 1.0000 0.0000 | 10.0000 交換兩行 1.0000 0.0000 -1.0000 | 0.0000 0.0000 2.0000 -1.0000 | 0.0000 0.0000 1.0000 0.0000 | 10.0000 消元 1.0000 0.0000 -1.0000 | 0.0000 0.0000 1.0000 -0.5000 | 0.0000 0.0000 0.0000 0.5000 | 10.0000 位置:row_pos = 2, col_pos = 2 選主元 1.0000 0.0000 -1.0000 | 0.0000 0.0000 1.0000 -0.5000 | 0.0000 0.0000 0.0000 0.5000 | 10.0000 交換兩行 1.0000 0.0000 -1.0000 | 0.0000 0.0000 1.0000 -0.5000 | 0.0000 0.0000 0.0000 0.5000 | 10.0000 消元 1.0000 0.0000 0.0000 | 20.0000 0.0000 1.0000 0.0000 | 10.0000 0.0000 0.0000 1.0000 | 20.0000 方程組有解 方程組及其解 1.0000 0.0000 0.0000 | 20.0000 0.0000 1.0000 0.0000 | 10.0000 0.0000 0.0000 1.0000 | 20.0000 x[0] = 20.0000 x[1] = 10.0000 x[2] = 20.0000