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# Ridge Regression

Unsolved
###### Supervised

Difficulty: 4 | Problem written by ankita
Regularization is a form of regression that discourages learning a more complex or flexible model to avoid the risk of overfitting. Ridge regression is implemented by adding an additional term in the loss function. Here, the loss function is the linear least-squares function and the regularization is given by the L2-norm:

L(W,α)= $$||XW-y||^{2}+\alpha||W||^{2}$$

The partial derivative of the loss function is calculated with respect to ‘W’ and the function is set as equal to zero to get the desired ‘W’. The ‘W’ that we get after applying the math is:

W=$$(X^{T}X+\alpha I)^{-1}X^{T}y$$

Where I is an identity matrix and α is defined by you.

We expect you to implement this algorithm manually and return the ‘W’ corresponding to the best-suited α and the loss for the corresponding parameters.

Input:

X: an array of training examples.

y: an array of output corresponding to each training example

alpha: Different values of α for which you have to get minimum loss

Output:

For each α, calculate the 'W' and hence the loss according to the function above on the whole training data and return the α, loss score and 'W' for the α with minimum loss on the training data.

Output should be in the following order:

α, loss score, numpy array of 'W'.

##### Sample Input:
<class 'list'>
X: [[0.60125408, 0.12577945, 0.01411056, 0.0936978, 0.89758782, 0.93564844, 0.8950285, 0.47727655, 0.71737809, 0.59242012], [0.13858243, 0.24482032, 0.86234713, 0.33979516, 0.0889971, 0.64927903, 0.57949765, 0.38865498, 0.02500174, 0.78624164], [0.46325961, 0.30377005, 0.15942722, 0.29213869, 0.59723249, 0.23040769, 0.38858347, 0.39792989, 0.22995737, 0.2646458], [0.26977591, 0.10918761, 0.21551369, 0.05295569, 0.84376132, 0.41889707, 0.12817272, 0.95816636, 0.95781923, 0.6110987], [0.73695696, 0.4750288, 0.82283346, 0.66565624, 0.37338998, 0.78591842, 0.0742858, 0.8773378, 0.48120651, 0.48274888], [0.09708786, 0.91395461, 0.76595178, 0.21224482, 0.15616675, 0.85005413, 0.70310046, 0.88231817, 0.74145004, 0.6024671], [0.75903593, 0.46548889, 0.31014249, 0.87254449, 0.27189493, 0.60013148, 0.43970967, 0.24510671, 0.42089798, 0.32563036], [0.62350623, 0.69931332, 0.96678008, 0.16620784, 0.21867862, 0.07789741, 0.9754635, 0.00814793, 0.87632045, 0.78894852], [0.93176233, 0.94406265, 0.27014565, 0.85860165, 0.53244571, 0.7849823, 0.47061634, 0.82533955, 0.97938773, 0.5625293], [0.30010037, 0.92693908, 0.23358359, 0.59492493, 0.14378321, 0.79335955, 0.54795122, 0.93509142, 0.49911903, 0.1223535], [0.12125732, 0.03845552, 0.53730161, 0.33617737, 0.00424432, 0.68671698, 0.84538236, 0.63718911, 0.99249623, 0.11882383], [0.34461216, 0.3353819, 0.96411776, 0.65207153, 0.24999972, 0.37552798, 0.47608931, 0.72491517, 0.80095516, 0.68978142], [0.18362188, 0.58009584, 0.31087527, 0.84663187, 0.49291746, 0.88991947, 0.81423266, 0.00850095, 0.13322052, 0.85356227], [0.04315464, 0.50934197, 0.01864857, 0.64816, 0.11961158, 0.89168548, 0.02568152, 0.47235023, 0.29562819, 0.7476345], [0.44860421, 0.14621354, 0.34438205, 0.68228521, 0.31818425, 0.91887658, 0.74396, 0.45496131, 0.03400659, 0.14556801], [0.87777354, 0.1715586, 0.12218999, 0.07434893, 0.24157273, 0.76799222, 0.38555271, 0.03912091, 0.37887198, 0.04369867], [0.70235542, 0.85722687, 0.61369535, 0.51259233, 0.91769692, 0.04260091, 0.92715519, 0.11154074, 0.86136391, 0.17674612], [0.64574304, 0.70516763, 0.01899496, 0.29888788, 0.20827288, 0.06270067, 0.28274384, 0.41546589, 0.30170273, 0.49650167], [0.06605403, 0.22370203, 0.72766904, 0.27268386, 0.71954316, 0.67180046, 0.018005, 0.62971642, 0.40960662, 0.2556009], [0.87758445, 0.9914289, 0.43224018, 0.87862905, 0.14434139, 0.94006928, 0.39777724, 0.00741952, 0.32963568, 0.53465108]]
<class 'list'>
Y: [[0.28536552], [0.34221503], [0.84590637], [0.26964398], [0.27359041], [0.9442081], [0.71474058], [0.18775526], [0.68799382], [0.17606394], [0.55740976], [0.9541375], [0.38676104], [0.48218884], [0.83872929], [0.75201683], [0.75870764], [0.60631138], [0.26194846], [0.73325989]]
<class 'list'>
alpha: [1, 5, 0.1]

##### Expected Output:
<class 'tuple'>
(0.1, 1.3435677397481878, array([[ 0.30920673], [ 0.00949388], [ 0.08465373], [ 0.26662866], [-0.00174554], [ 0.05644303], [ 0.26276322], [ 0.18520228], [-0.01781252], [-0.05082192]]))

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