您好,登錄后才能下訂單哦!
本篇內(nèi)容介紹了“python模擬支持向量機(jī)舉例分析”的有關(guān)知識(shí),在實(shí)際案例的操作過程中,不少人都會(huì)遇到這樣的困境,接下來就讓小編帶領(lǐng)大家學(xué)習(xí)一下如何處理這些情況吧!希望大家仔細(xì)閱讀,能夠?qū)W有所成!
1、線性可分支持向量機(jī),或硬間隔支持向量機(jī)。構(gòu)建它的條件是訓(xùn)練數(shù)據(jù)線性可分。其學(xué)習(xí)策略是最大間隔法??梢员硎緸橥苟我?guī)劃問題
2、現(xiàn)實(shí)中訓(xùn)練數(shù)據(jù)是線性可分的情形較少,訓(xùn)練數(shù)據(jù)往往是近似線性可分的,這時(shí)使用線性支持向量機(jī),或軟間隔支持向量機(jī)。線性支持向量機(jī)是最基本的支持向量機(jī)。對(duì)于噪聲或例外,通過引入松弛變量,使其“可分”,
3、對(duì)于輸入空間中的非線性分類問題,可以通過非線性變換將它轉(zhuǎn)化為某個(gè)高維特征空間中的線性分類問題,在高維特征空間中學(xué)習(xí)線性支持向量機(jī)。由于在線性支持向量機(jī)學(xué)習(xí)的對(duì)偶問題里,目標(biāo)函數(shù)和分類決策函數(shù)都只涉及實(shí)例與實(shí)例之間的內(nèi)積,所以不需要顯式地指定非線性變換,而是用核函數(shù)來替換當(dāng)中的內(nèi)積。核函數(shù)表示,通過一個(gè)非線性轉(zhuǎn)換后的兩個(gè)實(shí)例間的內(nèi)積。
4、SMO算法。SMO算法是支持向量機(jī)學(xué)習(xí)的一種快速算法,其特點(diǎn)是不斷地將原二次規(guī)劃問題分解為只有兩個(gè)變量的二次規(guī)劃子問題,并對(duì)子問題進(jìn)行解析求解,直到所有變量滿足KKT條件為止。這樣通過啟發(fā)式的方法得到原二次規(guī)劃問題的最優(yōu)解。因?yàn)樽訂栴}有解析解,所以每次計(jì)算子問題都很快,雖然計(jì)算子問題次數(shù)很多,但在總體上還是高效的。
import numpy as np import pandas as pd from sklearn.datasets import load_iris from sklearn.model_selection import train_test_split import matplotlib.pyplot as plt from sklearn.svm import SVC def create_data(): iris = load_iris() df = pd.DataFrame(iris.data, columns=iris.feature_names) df['label'] = iris.target df.columns = [ 'sepal length', 'sepal width', 'petal length', 'petal width', 'label' ] data = np.array(df.iloc[:100, [0, 1, -1]]) for i in range(len(data)): if data[i, -1] == 0: data[i, -1] = -1 # print(data) return data[:, :2], data[:, -1] X, y = create_data() X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.25) clf = SVC() # 下邊的參數(shù)設(shè)置了線性模擬,設(shè)置之后才可以畫出模擬函數(shù)的圖 # clf = SVC(kernel='linear') clf.fit(X_train, y_train) print("訓(xùn)練集評(píng)分:{}".format(str(clf.score(X_test, y_test)*100)+"%")) # 上邊設(shè)置線性之后,下邊的注釋代碼才能使用 # x_points = np.arange(4, 8) # y_ = -(clf.coef_[0][0]*x_points + clf.intercept_)/clf.coef_[0][1] # plt.plot(x_points, y_) plt.scatter(X[:50, 0], X[:50, 1], label='-1') plt.scatter(X[50:, 0], X[50:, 1], label='1') plt.legend() plt.show()
結(jié)果:
數(shù)據(jù)點(diǎn):
線性模擬結(jié)果圖:
訓(xùn)練集評(píng)分:100.0%
import numpy as np import pandas as pd from sklearn.datasets import load_iris from sklearn.model_selection import train_test_split import matplotlib.pyplot as plt def create_data(): iris = load_iris() df = pd.DataFrame(iris.data, columns=iris.feature_names) df['label'] = iris.target df.columns = [ 'sepal length', 'sepal width', 'petal length', 'petal width', 'label' ] data = np.array(df.iloc[:100, [0, 1, -1]]) for i in range(len(data)): if data[i, -1] == 0: data[i, -1] = -1 # print(data) return data[:, :2], data[:, -1] X, y = create_data() X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.25) plt.scatter(X[:50, 0], X[:50, 1], label='-1') plt.scatter(X[50:, 0], X[50:, 1], label='1') plt.legend() plt.show() class SVM: def __init__(self, max_iter=100, kernel='linear'): self.max_iter = max_iter self._kernel = kernel def init_args(self, features, labels): self.m, self.n = features.shape self.X = features self.Y = labels self.b = 0.0 # 將Ei保存在一個(gè)列表里 self.alpha = np.ones(self.m) self.E = [self._E(i) for i in range(self.m)] # 松弛變量 self.C = 1.0 def _KKT(self, i): y_g = self._g(i) * self.Y[i] if self.alpha[i] == 0: return y_g >= 1 elif 0 < self.alpha[i] < self.C: return y_g == 1 else: return y_g <= 1 # g(x)預(yù)測(cè)值,輸入xi(X[i]) def _g(self, i): r = self.b for j in range(self.m): r += self.alpha[j] * self.Y[j] * self.kernel(self.X[i], self.X[j]) return r # 核函數(shù) def kernel(self, x1, x2): if self._kernel == 'linear': return sum([x1[k] * x2[k] for k in range(self.n)]) elif self._kernel == 'poly': return (sum([x1[k] * x2[k] for k in range(self.n)]) + 1)**2 return 0 # E(x)為g(x)對(duì)輸入x的預(yù)測(cè)值和y的差 def _E(self, i): return self._g(i) - self.Y[i] def _init_alpha(self): # 外層循環(huán)首先遍歷所有滿足0<a<C的樣本點(diǎn),檢驗(yàn)是否滿足KKT index_list = [i for i in range(self.m) if 0 < self.alpha[i] < self.C] # 否則遍歷整個(gè)訓(xùn)練集 non_satisfy_list = [i for i in range(self.m) if i not in index_list] index_list.extend(non_satisfy_list) for i in index_list: if self._KKT(i): continue E1 = self.E[i] # 如果E2是+,選擇最小的;如果E2是負(fù)的,選擇最大的 if E1 >= 0: j = min(range(self.m), key=lambda x: self.E[x]) else: j = max(range(self.m), key=lambda x: self.E[x]) return i, j def _compare(self, _alpha, L, H): if _alpha > H: return H elif _alpha < L: return L else: return _alpha def fit(self, features, labels): self.init_args(features, labels) for t in range(self.max_iter): # train i1, i2 = self._init_alpha() # 邊界 if self.Y[i1] == self.Y[i2]: L = max(0, self.alpha[i1] + self.alpha[i2] - self.C) H = min(self.C, self.alpha[i1] + self.alpha[i2]) else: L = max(0, self.alpha[i2] - self.alpha[i1]) H = min(self.C, self.C + self.alpha[i2] - self.alpha[i1]) E1 = self.E[i1] E2 = self.E[i2] # eta=K11+K22-2K12 eta = self.kernel(self.X[i1], self.X[i1]) + self.kernel( self.X[i2], self.X[i2]) - 2 * self.kernel(self.X[i1], self.X[i2]) if eta <= 0: # print('eta <= 0') continue alpha2_new_unc = self.alpha[i2] + self.Y[i2] * ( E1 - E2) / eta #此處有修改,根據(jù)書上應(yīng)該是E1 - E2,書上130-131頁 alpha2_new = self._compare(alpha2_new_unc, L, H) alpha1_new = self.alpha[i1] + self.Y[i1] * self.Y[i2] * ( self.alpha[i2] - alpha2_new) b1_new = -E1 - self.Y[i1] * self.kernel(self.X[i1], self.X[i1]) * ( alpha1_new - self.alpha[i1]) - self.Y[i2] * self.kernel( self.X[i2], self.X[i1]) * (alpha2_new - self.alpha[i2]) + self.b b2_new = -E2 - self.Y[i1] * self.kernel(self.X[i1], self.X[i2]) * ( alpha1_new - self.alpha[i1]) - self.Y[i2] * self.kernel( self.X[i2], self.X[i2]) * (alpha2_new - self.alpha[i2]) + self.b if 0 < alpha1_new < self.C: b_new = b1_new elif 0 < alpha2_new < self.C: b_new = b2_new else: # 選擇中點(diǎn) b_new = (b1_new + b2_new) / 2 # 更新參數(shù) self.alpha[i1] = alpha1_new self.alpha[i2] = alpha2_new self.b = b_new self.E[i1] = self._E(i1) self.E[i2] = self._E(i2) return 'train done!' def predict(self, data): r = self.b for i in range(self.m): r += self.alpha[i] * self.Y[i] * self.kernel(data, self.X[i]) return 1 if r > 0 else -1 def score(self, X_test, y_test): right_count = 0 for i in range(len(X_test)): result = self.predict(X_test[i]) if result == y_test[i]: right_count += 1 return right_count / len(X_test) def _weight(self): # linear model yx = self.Y.reshape(-1, 1) * self.X self.w = np.dot(yx.T, self.alpha) return self.w svm = SVM(max_iter=200) svm.fit(X_train, y_train) print("評(píng)分:{}".format(svm.score(X_test, y_test)))
“python模擬支持向量機(jī)舉例分析”的內(nèi)容就介紹到這里了,感謝大家的閱讀。如果想了解更多行業(yè)相關(guān)的知識(shí)可以關(guān)注億速云網(wǎng)站,小編將為大家輸出更多高質(zhì)量的實(shí)用文章!
免責(zé)聲明:本站發(fā)布的內(nèi)容(圖片、視頻和文字)以原創(chuàng)、轉(zhuǎn)載和分享為主,文章觀點(diǎn)不代表本網(wǎng)站立場(chǎng),如果涉及侵權(quán)請(qǐng)聯(lián)系站長(zhǎng)郵箱:is@yisu.com進(jìn)行舉報(bào),并提供相關(guān)證據(jù),一經(jīng)查實(shí),將立刻刪除涉嫌侵權(quán)內(nèi)容。