20250604

228-15.py

@@ -0,0 +1,60 @@
+def Norm(x,v):
+    if len(x[0]) == 1:
+        if v == 1:
+            return sum([abs(i[0]) for i in x])
+        elif v == 2:
+            return (sum([i[0]**2 for i in x]))**0.5
+        elif v == float("inf"):
+            return max([abs(i[0]) for i in x])
+    else:
+        if v == 1:
+            return max([sum([abs(x[i][j]) for i in range(len(x))]) for j in range(len(x[0]))])
+        elif v == float("inf"):
+            return max([sum([abs(i) for i in x[j]]) for j in range(len(x))])
+    return None
+
+
+def Det(A):
+    if len(A) == 2:
+        return A[0][0] * A[1][1] - A[0][1] * A[1][0]
+    det = 0
+    for c in range(len(A)):
+        sub_matrix = [row[:c] + row[c+1:] for row in A[1:]]
+        det += ((-1) ** c) * A[0][c] * Det(sub_matrix)
+    return det
+
+def Inverse(A):
+    n = len(A)
+    # 计算代数余子式矩阵
+    B = [[0 for i in range(n)] for j in range(n)]
+    for i in range(n):
+        for j in range(n):
+            minor = [row[:j] + row[j+1:] for row in (A[:i] + A[i+1:])]
+            B[j][i] = ((-1) ** (i + j)) * sum(minor[k][l] * (-1) ** (k + l) for k in range(n - 1) for l in range(n - 1))
+    det = Det(A)
+    print(det)
+    if det == 0:
+        print("矩阵不可逆")
+        return None
+    A_inv = [[B[i][j] / det for j in range(n)] for i in range(n)]
+    return A_inv
+
+def Cond(A,v):
+    inv_A = Inverse(A)
+    print(inv_A,Norm(A, v), Norm(inv_A, v))
+    return Norm(A, v) * Norm(inv_A, v)
+
+
+if __name__ == "__main__":
+    A = [
+        [1,2],
+        [1.001,2.001]
+    ]
+
+    print(f"矩阵A的条件数为: {Cond(A, float('inf')):.5f}")
+
+    A = [
+        [1,2],
+        [3,4]
+    ]
+    print(f"矩阵A的条件数为: {Cond(A, float('inf')):.5f}")