My question is about the lab in Machine Learning Specialization, and the “Optional Lab - Gradient Descent”
In the lab, the function compute_gradient is supposed to compute the gradient. The formulas are given as
\begin{align}
\frac{\partial J(w,b)}{\partial w} &= \frac{1}{m} \sum\limits_{i = 0}^{m-1} (f_{w,b}(x^{(i)}) - y^{(i)})x^{(i)} \tag{4}\\
\frac{\partial J(w,b)}{\partial b} &= \frac{1}{m} \sum\limits_{i = 0}^{m-1} (f_{w,b}(x^{(i)}) - y^{(i)}) \tag{5}\\
\end{align}
The code was defined as follows,
def compute_gradient(x, y, w, b):
"""
Computes the gradient for linear regression
Args:
x (ndarray (m,)): Data, m examples
y (ndarray (m,)): target values
w,b (scalar) : model parameters
Returns
dj_dw (scalar): The gradient of the cost w.r.t. the parameters w
dj_db (scalar): The gradient of the cost w.r.t. the parameter b
"""
# Number of training examples
m = x.shape[0]
dj_dw = 0
dj_db = 0
for i in range(m):
f_wb = w * x[i] + b # linear regression
dj_dw_i = (f_wb - y[i]) * x[i]
dj_db_i = f_wb - y[i]
dj_db += dj_db_i
dj_dw += dj_dw_i
dj_dw = dj_dw / m # what's happening here?
dj_db = dj_db / m # what's happening here?
return dj_dw, dj_db
Where is the 1/m from formulas (4) and (5) given? The code implementation looks different than the formulas, I’m confused about this step. Thanks for any help
