解释python代码np.zeros(self.problem.numberOfFeatures)
时间: 2024-05-20 20:10:10 浏览: 8
np.zeros(self.problem.numberOfFeatures) 是一个用于初始化数组的 numpy 函数,它创建一个由 0 组成的数组,该数组的长度等于 self.problem.numberOfFeatures。其中 self.problem.numberOfFeatures 是一个属性或变量,它存储了要创建的数组的长度或大小。此代码中使用的numpy函数的名称是 zeros,它是创建指定形状和类型的全零数组的函数。在此例中,创建的全零数组是一维数组,长度等于 self.problem.numberOfFeatures。
相关问题
BB方法迭代格式,给出BB方法的python代码
BB方法是一种求解整数规划的分枝定界算法,其迭代格式如下:
1. 初始化问题,并将其添加到问题队列中
2. 从问题队列中选择一个问题进行求解
3. 对问题进行分枝,生成子问题,并将其添加到问题队列中
4. 对分枝后的子问题进行求解,并更新下界和最优解
5. 如果问题队列为空或者下界大于等于当前最优解,则停止迭代,输出当前最优解
以下是BB方法的Python代码实现:
```python
import numpy as np
class Problem:
def __init__(self, c, A, b, x):
self.c = c
self.A = A
self.b = b
self.x = x
self.z = np.dot(c, x)
self.lb = -np.inf
self.ub = np.inf
def branch(self, idx):
x1 = self.x.copy()
x1[idx] = 0
p1 = Problem(self.c, self.A, self.b, x1)
x2 = self.x.copy()
x2[idx] = 1
p2 = Problem(self.c, self.A, self.b, x2)
return [p1, p2]
def bb(c, A, b):
n = c.shape[0]
x = np.zeros(n)
root = Problem(c, A, b, x)
queue = [root]
opt = None
while len(queue) > 0:
problem = queue.pop(0)
if problem.z <= problem.lb:
continue
if problem.z < problem.ub:
idx = np.argmax(np.abs(problem.c))
subproblems = problem.branch(idx)
for subproblem in subproblems:
subproblem.lb = problem.lb
subproblem.ub = problem.ub
if np.all(np.dot(subproblem.A, subproblem.x) <= subproblem.b):
subproblem.z = np.dot(subproblem.c, subproblem.x)
if subproblem.z > problem.lb:
problem.lb = subproblem.z
if subproblem.z < problem.ub:
queue.append(subproblem)
problem.ub = subproblem.z
opt = subproblem
return opt.x, opt.z
```
其中,`Problem`类表示一个整数规划问题,包括目标函数系数`c`,约束矩阵`A`,约束右边向量`b`,当前解`x`,当前最优目标函数值`z`,以及下界和上界。`bb`函数是BB方法的主函数,其中`queue`表示问题队列,`opt`表示最优解。在函数中,首先初始化根节点,然后将其添加到问题队列中。在每一次迭代中,从问题队列中选择一个问题进行求解,并对其进行分枝,生成子问题,并将其添加到问题队列中。对分枝后的子问题进行求解,并更新下界和最优解。如果问题队列为空或者下界大于等于当前最优解,则停止迭代,输出当前最优解。
jda算法的python代码实现
JDA算法(Joint Distribution Adaptation)是一种域适应方法,它通过对源域数据和目标域数据分别建模,利用最大化它们之间的相似性来实现跨域知识转移。本文将介绍如何使用Python实现JDA算法。
首先,需要导入以下库:numpy,scipy,sklearn,和Cython。其中Cython是Python语言的扩展,主要用于编写C语言的扩展模块。
初始化函数中,我们需要指定两个域的标签、源域特征和目标域特征。在建模之前,需要计算出两个域的协方差矩阵。
然后,我们需要用高斯核函数来计算源域和目标域的核矩阵。接着,通过解决广义特征值问题来获取最大化领域间距离的变换矩阵,该矩阵可以将源域和目标域的特征转换成低维表示。
最后,在训练完变换矩阵后,我们可以将它应用于测试数据,以获得更好的分类效果。
下面是JDA算法的Python代码实现:
```
import numpy as np
from scipy import linalg
from sklearn.metrics.pairwise import rbf_kernel
from sklearn.base import BaseEstimator, TransformerMixin
from sklearn.utils import check_array, check_random_state
from scipy.spatial.distance import cdist
from sklearn.decomposition import PCA
from sklearn.linear_model import LogisticRegression
try:
from .jda_cython import inner_jda
except ImportError:
print('Cython not found. To compile cython .pyx file you need '
'to run command "python setup.py build_ext --inplace" in'
'"jda_cython" folder')
from .jda_python import inner_jda
class JDA(BaseEstimator, TransformerMixin):
def __init__(self, dim=30, n_iter=10, gamma=1.0, kernel='rbf', random_state=None):
self.dim = dim
self.n_iter = n_iter
self.gamma = gamma
self.kernel = kernel
self.random_state = random_state
def fit(self, X, y, Xt=None, yt=None):
'''
Parameters
----------
X : array-like, shape (n_samples, n_features)
Source data
y : array-like, shape (n_samples, )
Source labels
Xt : array-like, shape (n_target_samples, n_features), optional
Target data
yt : array-like, shape (n_target_samples,), optional
Target labels
Returns
-------
self : object
Returns self.
'''
if Xt is None:
# use the source data as target data as well
Xt = X
yt = y
random_state = check_random_state(self.random_state)
# compute the covariance matrices of the source and target domains
Cs = np.cov(X.T)
Ct = np.cov(Xt.T)
# compute the kernel matrices of the source and target domains
Ks = rbf_kernel(X, gamma=self.gamma)
Kt = rbf_kernel(Xt, X, gamma=self.gamma)
self.scaler_ = PCA(n_components=self.dim).fit(
np.vstack((X, Xt)))
Xs_pca = self.scaler_.transform(X)
Xt_pca = self.scaler_.transform(Xt)
X_pca = np.vstack((Xs_pca, Xt_pca))
V_src = np.eye(Xs_pca.shape[1])
V_trg = np.eye(Xt_pca.shape[1])
for i in range(self.n_iter):
W = JDA._calculate_projection(
X_pca, np.array(source_labels+target_labels), V_src, V_trg, Ks, Kt)
Xs_pca = Xs_pca.dot(W)
Xt_pca = Xt_pca.dot(W)
self.W_ = W
self.Xs_pca_ = Xs_pca
self.Xt_pca_ = Xt_pca
self.clf_ = LogisticRegression(random_state=random_state,
solver='lbfgs',
max_iter=1000,
)
self.clf_.fit(Xs_pca, y)
return self
def transform(self, X):
"""Transforms data X using the fitted models
Parameters
----------
X : array-like, shape (n_samples, n_features)
Data to transform
Returns
-------
Xt_new : array, shape (n_samples, n_components)
Transformed data
"""
return self.scaler_.transform(X).dot(self.W_)
def fit_transform(self, X, y, Xt=None, yt=None):
"""Fit and transform data X using the fitted models
Parameters
----------
X : array-like, shape (n_samples, n_features)
Data to transform
y : array-like, shape (n_samples, )
Labels
Xt : array-like, shape (n_target_samples, n_features), optional
Target data
yt : array-like, shape (n_target_samples,), optional
Target labels
Returns
-------
Xt_new : array, shape (n_target_samples, n_components)
Transformed data
"""
self.fit(X, y, Xt, yt)
return self.transform(Xt)
@staticmethod
def _calculate_projection(X, Y, V_src, V_trg, Ks, Kt):
n = X.shape[0]
ns = Ks.shape[0]
nt = Kt.shape[0]
eps = 1e-4
H_s = np.eye(ns) - 1.0 / ns * np.ones((ns, ns))
H_t = np.eye(nt) - 1.0 / nt * np.ones((nt, nt))
A = np.vstack((np.hstack((Ks + eps * np.eye(ns), np.zeros((ns, nt)))),
np.hstack((np.zeros((nt, ns)), Kt + eps * np.eye(nt)))))
B = np.vstack((H_s, H_t))
# solve the generalized eigenvalue problem Ax = lambda Bx
lambda_, p = linalg.eig(A, B)
# sort eigenvalues in ascending order
idx = np.argsort(-lambda_.real)
lambda_ = lambda_[idx]
p = p[:, idx]
t = Y
c1 = 1.0 / ns * sum(p[:ns, :].T.dot(t == 1))
c2 = 1.0 / nt * sum(p[ns:, :].T.dot(t == -1))
MMD = sum(sum(p[:ns, :].T.dot(Ks).dot(p[:ns, :])) / ns ** 2
+ sum(p[ns:, :].T.dot(Kt).dot(p[ns:, :])) / nt ** 2
- 2 * sum(p[:ns, :].T.dot(Kt).dot(p[ns:, :])) / (ns * nt))
# calculate the optimal projection matrix
V = p[:ns, :].dot(np.diag(1.0 / lambda_[:ns])).dot(
p[:ns, :].T).dot(H_s - H_t).dot(p[ns:, :]).dot(
np.diag(1.0 / lambda_[ns:])).dot(p[ns:, :].T)
# calculate the transformation matrix
W = X.T.dot(V).dot(X)
return W
if __name__ == "__main__":
np.random.seed(1234)
# generate example data
n = 100
d = 100
X = np.random.randn(n, d)
y = np.concatenate((np.ones(n // 2, dtype=np.int), -np.ones(n // 2, dtype=np.int)))
Xs = X[:n // 2, :]
ys = y[:n // 2]
Xt = X[n // 2:, :]
yt = y[n // 2:]
# train and evaluate model
model = JDA(n_iter=10)
Xt_new = model.fit_transform(Xs, ys, Xt, yt)
clf = LogisticRegression(random_state=1234)
clf.fit(model.transform(Xs), ys)
print('Accuracy on source domain: {:.2f}%'.format(clf.score(model.transform(Xs), ys) * 100))
print('Accuracy on target domain: {:.2f}%'.format(clf.score(Xt_new, yt) * 100))
```
以上就是JDA算法的Python代码实现。我们可以使用上述代码来实现域适应问题中的知识转移。
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