Implementation of Gradient Descent for Energy Efficiency Prediction using Python
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Linear Regression with Gradient Descent is a good and simple method for time series prediction. One of the time series predictions that can be solved by this method is Energy Efficiency Prediction. And the purpose of this research article is to implement Linear Regression with Gradient Descent to predict the Heating Load (Y1). The programming language used for this case is using Python code. The data can be downloaded from https://archive.ics.uci.edu/ml/datasets/Energy+efficiency.

The training data used 50% from the dataset and testing data also used 50% from the dataset. The dataset has eight input data there is Relative Compactness (X1), Surface Area (X2), Wall Area (X3),  Roof Area (X4),  Overall Height (X5), Orientation (X6),  Glazing Area (X7), and Glazing Area (X8). This article will show a brief discussion of prediction results using Linear Regression with Gradient Descent.

DEVELOPMENT

Gradient Descent comes with some procedure that is:

  • Procedure
    • Start with random values
      • \theta = \theta_{}^{(0)} = ( {\theta_{0}}^{(0)}, {\theta_{1}}^{(0)}, ... {\theta_{d}}^{(0)} )
    • Slightly move \theta_{0}, ... \theta_{d} to reduce J(\theta)
      • \displaystyle \Large \theta _{i}^{k+1} = \theta _{i}^{k} - \alpha \left. \frac{\partial J( \theta )}{\partial \theta _{i} } \, \right|_{ \theta = \theta_{}^{k} }
      • k = k + 1
    • Keep doing step 2 until converges

Technologies Used

To solve this problem, it was used the Python 3 language with the following libraries:

  1. Pandas: Python library for data structures and statistical tools (McKinney, 2010).
  2. Numpy: The Python libraries for the base data structure used for data and model parameters were presented as Numpy arrays (Al-Shalabi et al., 2006).
  3. Sklearn (Hunter, 2007).

IMPLEMENTATION USING PYTHON CODE

The python code for this project is used one file with the name of the file is GradientDescentEnergy.py. We are using one file of Training and Testing data on the .csv file with name ENB2012_data.csv.

Import libraries:

import sys

import numpy
import pandas
import sklearn.metrics
import sklearn.model_selection
import sklearn.linear_model
import sklearn.preprocessing

Loading Dataset:

def load_train_test_data(train_ratio=.5):
    data = pandas.read_csv('./ENB2012_data.csv')
   
    feature_col = ['X1', 'X2', 'X3', 'X4', 'X5', 'X6', 'X7', 'X8']
    label_col = ['Y1']
    X = data[feature_col]
    y = data[label_col]

    return sklearn.model_selection.train_test_split(X, y, test_size = 1 - train_ratio, random_state=0)

Scale the Training and Testing Features

def scale_features(X_train, X_test, low=0, upp=1):
    minmax_scaler = sklearn.preprocessing.MinMaxScaler(feature_range=(low, upp)).fit(numpy.vstack((X_train, X_test)))
    X_train_scale = minmax_scaler.transform(X_train)
    X_test_scale = minmax_scaler.transform(X_test)
    return X_train_scale, X_test_scale

Gradient Descent Calculation

def gradient_descent(X, y, alpha = .001, iters = 100000, eps=1e-4):
    n, d = X.shape
    theta = numpy.zeros((d, 1))

    return theta

Prediction Function

def predict(X, theta):
    return numpy.dot(X, theta)

Main Function

def main(argv):
    X_train, X_test, y_train, y_test = load_train_test_data(train_ratio=.5)
    X_train_scale, X_test_scale = scale_features(X_train, X_test, 0, 1)

    theta = gradient_descent(X_train_scale, y_train)
    y_hat = predict(X_train_scale, theta)
    print("Linear train R^2: %f" % (sklearn.metrics.r2_score(y_train, y_hat)))
    y_hat = predict(X_test_scale, theta)
    print("Linear test R^2: %f" % (sklearn.metrics.r2_score(y_test, y_hat)))

if __name__ == "__main__":
    main(sys.argv)

RESULT AND DISCUSSION

This article shows the result of the experiment using some parameter value there is the value of alpha and maximum iteration. this experiment is aiming to find the optimum parameter value to predict the Heating Load (Y1).

Testing Value of Alpha

The process of testing the value of alpha was done one time, the value of alpha was 0.1 to 0.000001. The values of maximum iteration used constantly that is 1000. The optimum value of alpha can be seen from the R2 result. The test results on the R2 value shown in Table 1. The chart of R2 value changes according to the value of alpha can be seen in Figure 1.

Table 1. R2 value from Testing Value of Alpha

Value of AlphaR Square
TrainTest
0.10.9201430.896159
0.010.9033760.880996
0.0010.4967690.460076
0.0001-2.993605-3.154529
0.00001-4.593513-4.765798

The testing results value of alpha in Table 1 indicates that the best R2 value was obtained with value of alpha is 0.1.

Figure 1. Chart of R2 Value from Every Alpha
Figure 1. (Detail) Chart of R2 Value from Training on Every Alpha
Figure 1. (Detail) Chart of R2 Value from Testing on Every Alpha

Testing Value of Maximum Iteration

The process of testing the value of Maximum Iteration was done one time, the value of Maximum Iteration was 10 to 10000. The values of alpha used from the previous testing that is 0.1. The optimum value of Maximum Iteration can be seen from the R2 result. The test results on the R2 value shown in Table 2. The chart of R2 value changes according to the value of Maximum Iteration can be seen in Figure 2.

Table 2. R2 value from Testing Value of Maximum Iteration

Value of Max
Iteration
R Square
TrainTest
100.5292250.497496
1000.9035130.881109
10000.9201430.896159
100000.9210270.900045
1000000.921560.900637

The testing results value of Maximum Iteration in Table 2 indicate that the best R2 value was obtained with a value of Maximum Iteration is 10000. Because of that, I choose maximum iteration at 10,000 because after that nothing significant improvement of R2 value. So, the optimum maximum generation is 10,000 because it also considers the value running time.

Figure 2. Chart of R2 Value from Testing Value of Maximum Iteration

Result Analysis

We can see from Figure 2, the R2 value accuracy from training data at the blue line and the R2 value from testing data at the orange line. From the testing and training data, the optimal value of alpha is 0.1 and the optimum maximum iteration is 10000. Form the testing parameter value, Linear regression using Gradient Descent can predict the Heating Load (Y1) with R2 value 0.92156 for training and 0.900637 for testing. The detail result form this experiment can see in the figure below:

Theta:
 [[ 2.32952123]
 [ 2.97557991]
 [ 8.4017958 ]
 [19.42200572]
 [-0.32337598]
 [ 7.52095841]
 [ 0.86006606]]
Linear train R^2: 0.921027
Linear test R^2: 0.900045
Mean Squared Error Test : 10.275206
Mean Absolute Error Test : 2.369451

So we can write the formulation to find Heating Load (Y1) as follow:

Y=X_1 θ_1+X_2 θ_2+ X_3 θ_3+ X_4 θ_4+ X_5 θ_5+ X_6 θ_6+ X_7 θ_7+ X_8 θ_8 Y = X_1 (2.32952123)+X_2 (2.97557991)+ X_3 (8.4017958)+ X_4 (2.92006335)+ X_5 (19.42200572)+ X_6 (-0.32337598)+ X_7 (7.52095841)+ X_8 (0.86006606)

Read Also: Implementation of K-Nearest Neighbors (KNN) For Iris Classification Using Python 3

You can get the full code using Python by request via Direct Message or Email.

REFERENCES

Al-Shalabi, R., Kanaan, G., & Gharaibeh, M. H. (2006). Arabic Text Categorization Using kNN Algorithm. Proceedings of The 4th International Multiconference on Computer Science and Information Technology, 5–7.

Hunter, J. D. (2007). Matplotlib: A 2D Graphics Environment. Computing in Science & Engineering, 9(3), 90–95. https://doi.org/10.1109/MCSE.2007.55

Lotte, F., Congedo, M., Lécuyer, A., Lamarche, F., & Arnaldi, B. (2007). A review of classification algorithms for EEG-based brain-computer interfaces. Journal of Neural Engineering, 4(2). https://doi.org/10.1088/1741-2560/4/2/R01

McKinney, W. (2010). Data Structures for Statistical Computing in Python. Proceedings of the 9th Python in Science Conference, 1697900(Scipy), 51–56. Retrieved from http://conference.scipy.org/proceedings/scipy2010/mckinney.html

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Written by Ida Wahyuni

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