# π Exercise M4.01ΒΆ

The aim of this exercise is two-fold:

understand the parametrization of a linear model;

quantify the fitting accuracy of a set of such models.

We will reuse part of the code of the course to:

load data;

create the function representing a linear model.

## PrerequisitesΒΆ

### Data loadingΒΆ

Note

If you want a deeper overview regarding this dataset, you can refer to the Appendix - Datasets description section at the end of this MOOC.

```
import pandas as pd
penguins = pd.read_csv("../datasets/penguins_regression.csv")
feature_name = "Flipper Length (mm)"
target_name = "Body Mass (g)"
data, target = penguins[[feature_name]], penguins[target_name]
```

### Model definitionΒΆ

```
def linear_model_flipper_mass(
flipper_length, weight_flipper_length, intercept_body_mass
):
"""Linear model of the form y = a * x + b"""
body_mass = weight_flipper_length * flipper_length + intercept_body_mass
return body_mass
```

## Main exerciseΒΆ

Given a vector of the flipper length, several weights and intercepts to plot several linear model that could fit our data. Use the above helper function to visualize both the model and data.

```
import numpy as np
flipper_length_range = np.linspace(data.min(), data.max(), num=300)
```

```
# Write your code here.
# weights = [...]
# intercepts = [...]
```

In the previous question, you were asked to create several linear models. The visualization allowed you to qualitatively assess if a model was better than another.

Now, you should come up with a quantitative measure which will indicate the goodness of fit of each linear model. This quantitative metric should result in a single scalar and allow you to pick up the best model.

```
def goodness_fit_measure(true_values, predictions):
# Write your code here.
# Define a measure indicating the goodness of fit of a model given the true
# values and the model predictions.
pass
```

```
# Uncomment the code below.
# for model_idx, (weight, intercept) in enumerate(zip(weights, intercepts)):
# target_predicted = linear_model_flipper_mass(data, weight, intercept)
# print(f"Model #{model_idx}:")
# print(f"{weight:.2f} (g / mm) * flipper length + {intercept:.2f} (g)")
# print(f"Error: {goodness_fit_measure(target, target_predicted):.3f}\n")
```