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April 14, 2018 17:41
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Use linear regression to analysis bending data
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import numpy as np | |
import matplotlib.pyplot as plt | |
from scipy.stats import t | |
def plotOne(x, y): | |
x = np.array(x) | |
y = np.array(y) | |
# https://en.wikipedia.org/wiki/Simple_linear_regression | |
# bx + a | |
head_b = np.sum((x - x.mean()) * (y - y.mean())) / np.sum((x - x.mean()) ** 2) | |
head_a = y.mean() - head_b * x.mean() | |
fit_y = head_b * x + head_a | |
r_square = np.sum((fit_y - y.mean()) ** 2) / np.sum((y - y.mean()) ** 2) | |
# confidence of slope and intercept | |
n = len(x) | |
var_b = np.sum((y - fit_y) ** 2) / (n + 2) / np.sum((x - x.mean()) ** 2) | |
intval_b = np.sqrt(var_b) * t.ppf(0.995, n - 2) | |
var_a = var_b * np.sum(x ** 2) / n | |
intval_a = np.sqrt(var_a) * t.ppf(0.995, n - 2) | |
# plot | |
text = '''\ | |
In 99% confidence | |
slope = {:.3}±{:.3} | |
intercept = {:.3}±{:.3} | |
r_squre = {:.3} | |
'''.format(head_b, intval_b, head_a, intval_a, r_square) | |
plt.text(.95, .05, text, | |
horizontalalignment='right', | |
verticalalignment='bottom', | |
transform=plt.gca().transAxes) | |
plt.plot(x, y, 'o', label="original data") | |
plt.plot(x, fit_y, label="fit line") | |
plt.legend(loc = 0) | |
# fix weight | |
length = [31.4,40.4,47.5,57.6,73.1] | |
data = [1.35007,1.44944,1.52843,1.63034,1.79341] | |
plotOne(length, data) | |
plt.title("Bending data for Fixed Weight = 5kg") | |
plt.xlabel("length(cm)") | |
plt.ylabel("Voltage (1000 * V)") | |
plt.savefig("bending1.jpg") | |
plt.show() | |
weight = [2,4,6,8,10] | |
data = [1.31440,1.51823,1.71952,1.91823,2.11444] | |
plotOne(weight, data) | |
plt.title("Bending data for Fixed Length = 58cm") | |
plt.xlabel("Weight (kg)") | |
plt.ylabel("Voltage (1000 * V)") | |
plt.savefig("bending2.jpg") | |
plt.show() |
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