human
Can you provide a code to 4 Linear regression and the other steps required given the following:
4 Linear regression
Using numpy, fit and evaluate the linear model $$\hat{w}, \hat{b} = \operatorname*{arg min}_{w,b} \| Xw + b - y \|_2^2.$$
Please define a class LinearRegression with two methods:
1. fit learn the parameters $w$ and $b$ of the model given the training examples.
2. predict gives the estimated number of likes of a post / tweet. That will be used to evaluate the model on the testing set.
To evaluate the classifier, create an accuracy(y_pred, y_true) function which computes the mean squared error $\frac1n \| \hat{y} - y \|_2^2$.
Hint: you may want to use the function scipy.sparse.linalg.spsolve()."
Please write code following the instructions in jupyter notebook style.
assistant
#Here is code to 4 Linear regression and the other steps required.

import scipy.sparse
class RidgeRegression(object):
    """Our ML model."""
    
    def __init__(self, alpha=0):
        "The class' constructor. Initialize the hyper-parameters."
        self.a = alpha
    
    def predict(self, X):
        """Return the predicted class given the features."""
        return np.sign(X.dot(self.w) + self.b)
    
    def fit(self, X, y):
        """Learn the model's parameters given the training data, the closed-form way."""
        n, d = X.shape
        self.b = np.mean(y)
        Ainv = np.linalg.inv(X.T.dot(X) + self.a * np.identity(d))
        self.w = Ainv.dot(X.T).dot(y - self.b)

    def loss(self, X, y, w=None, b=None):
        """Return the current loss.
        This method is not strictly necessary, but it provides
        information on the convergence of the learning process."""
        w = self.w if w is None else w  # The ternary conditional operator
        b = self.b if b is None else b  # makes those tests concise.
        import autograd.numpy as np  # See below for autograd.
        return np.linalg.norm(np.dot(X, w) + b - y)**2 + self.a * np.linalg.norm(w, 2)**2