PYTHON

Logistic Regression with a Neural Network mindset python example

import numpy as np
import matplotlib.pyplot as plt
import h5py
import scipy
from PIL import Image
from scipy import ndimage

%matplotlib inline

Logistic Regression with a Neural Network mindset python example

- a training set of m_train images labeled as cat (y=1) or non-cat (y=0)
- a test set of m_test images labeled as cat or non-cat
- each image is of shape (num_px, num_px, 3) where 3 is for the 3 channels (RGB). Thus, each image is square (height = num_px) and (width = num_px).

Logistic Regression with a Neural Network mindset python example

# Loading the data (cat/non-cat)
train_set_x_orig, train_set_y, test_set_x_orig, test_set_y, classes = load_dataset()

Logistic Regression with a Neural Network mindset python example

y = [1], it's a 'cat' picture.

Logistic Regression with a Neural Network mindset python example

- m_train (number of training examples)
- m_test (number of test examples)
- num_px (= height = width of a training image)

Logistic Regression with a Neural Network mindset python example

Number of training examples: m_train = 209
Number of testing examples: m_test = 50
Height/Width of each image: num_px = 64
Each image is of size: (64, 64, 3)
train_set_x shape: (209, 64, 64, 3)
train_set_y shape: (1, 209)
test_set_x shape: (50, 64, 64, 3)
test_set_y shape: (1, 50)

Logistic Regression with a Neural Network mindset python example

X_flatten = X.reshape(X.shape[0], -1).T      # X.T is the transpose of X

Logistic Regression with a Neural Network mindset python example

train_set_x_flatten shape: (12288, 209)
train_set_y shape: (1, 209)
test_set_x_flatten shape: (12288, 50)
test_set_y shape: (1, 50)
sanity check after reshaping: [17 31 56 22 33]

Logistic Regression with a Neural Network mindset python example

train_set_x = train_set_x_flatten/255.
test_set_x = test_set_x_flatten/255.

Logistic Regression with a Neural Network mindset python example

- Initialize the parameters of the model
- Learn the parameters for the model by minimizing the cost  
- Use the learned parameters to make predictions (on the test set)
- Analyse the results and conclude

Logistic Regression with a Neural Network mindset python example

print ("sigmoid([0, 2]) = " + str(sigmoid(np.array([0,2]))))

Logistic Regression with a Neural Network mindset python example

sigmoid([0, 2]) = [ 0.5         0.88079708]

Logistic Regression with a Neural Network mindset python example

dim = 2
w, b = initialize_with_zeros(dim)
print ("w = " + str(w))
print ("b = " + str(b))

Logistic Regression with a Neural Network mindset python example

# Example of a picture
index = 25
plt.imshow(train_set_x_orig[index])
print ("y = " + str(train_set_y[:, index]) + ", it's a '" + classes[np.squeeze(train_set_y[:, index])].decode("utf-8") +  "' picture.")