np.linalg.inv(Sw)
时间: 2023-11-19 12:28:16 浏览: 34
这段代码使用了 NumPy 库中的 linalg.inv() 函数,用于计算矩阵的逆。
具体来说,Sw 是一个矩阵,调用 linalg.inv(Sw) 将返回 Sw 的逆矩阵。
需要注意的是,只有方阵才有逆矩阵。如果 Sw 不是方阵,那么 linalg.inv() 函数将会抛出一个 LinAlgError 异常。如果 Sw 是奇异矩阵,也就是行列式为 0 的矩阵,那么 linalg.inv() 函数将会抛出一个 LinAlgError 异常。因此,在使用 linalg.inv() 函数之前,需要确保输入的矩阵 Sw 是方阵且非奇异矩阵。
相关问题
fisher判据分类数据的python代码
Sure, here is the Python code for Fisher's discriminant for classifying data:
```
import numpy as np
def fisher_discriminant(X, y):
"""
Fisher's linear discriminant for binary classification.
Arguments:
X: numpy array of shape (n_samples, n_features)
y: numpy array of shape (n_samples,)
Class labels, assumed to be binary (0 or 1).
Returns:
w: numpy array of shape (n_features,)
The weights for the linear discriminant function.
"""
# compute means of each class
mu0 = np.mean(X[y==0], axis=0)
mu1 = np.mean(X[y==1], axis=0)
# compute between-class scatter matrix
Sb = np.outer(mu1 - mu0, mu1 - mu0)
# compute within-class scatter matrix
Sw = np.zeros((X.shape[1], X.shape[1]))
for i in range(2):
Xi = X[y==i]
si = np.cov(Xi, rowvar=False)
Sw += (Xi.shape[0] - 1) * si
# solve the generalized eigenvalue problem for Sb and Sw
eigvals, eigvecs = np.linalg.eig(np.linalg.inv(Sw).dot(Sb))
# find the eigenvector with the largest eigenvalue
w = eigvecs[:, np.argmax(eigvals)]
return w
```
Hope this helps!
基于Fisher方法算法流程,Python实现Fisher线性判别方法
1. 数据预处理:读取数据、标准化数据、拆分训练集和测试集
2. 计算类内散度矩阵和类间散度矩阵
3. 计算矩阵特征值和特征向量
4. 选择前k个特征向量构建变换矩阵
5. 对训练数据进行变换
6. 训练分类器并对测试数据进行分类
Python实现Fisher线性判别方法的代码如下:
```python
import numpy as np
class FisherLDA:
def __init__(self, k_components=None):
self.k_components = k_components
def fit(self, X, y):
X = X.astype(float)
y = y.astype(int)
n_samples, n_features = X.shape
n_classes = len(np.unique(y))
mean_overall = np.mean(X, axis=0)
Sw = np.zeros((n_features, n_features))
Sb = np.zeros((n_features, n_features))
for i in range(n_classes):
Xi = X[y==i]
mean_class = np.mean(Xi, axis=0)
Sw += (Xi - mean_class).T.dot(Xi - mean_class)
Sb += len(Xi) * (mean_class - mean_overall).reshape(-1, 1).dot((mean_class - mean_overall).reshape(1, -1))
eigvalues, eigvectors = np.linalg.eig(np.linalg.inv(Sw).dot(Sb))
eigvectors = eigvectors.T
idxs = np.argsort(abs(eigvalues))[::-1]
eigvalues = eigvalues[idxs]
eigvectors = eigvectors[idxs]
if self.k_components is not None:
eigvectors = eigvectors[:self.k_components]
self.w = eigvectors.dot(np.linalg.inv(X.T.dot(X)).dot(X.T)).astype(float)
def transform(self, X):
return X.dot(self.w.T)
def predict(self, X):
X = self.transform(X)
return np.argmax(X, axis=1)
```
其中,`fit`方法实现了Fisher算法的主要流程,`transform`方法用于将数据进行变换,`predict`方法用于对数据进行分类。