### Daily Data Science Puzzle

import numpy as np # graphics data a = [[1, 1], [1, 0]] # stretch vectors b = [[2, 0], [0, 2]] c = np.matmul(a, b) print(c[0,1])

*What is the output of this puzzle?*

Numpy is a popular Python library for data science focusing on arrays, vectors, and matrices.

This puzzle shows an important application domain of matrix multiplication: Computer Graphics.

We create two matrices a and b. The first matrix a is the data matrix (e.g. consisting of two column vectors `(1,1)`

and `(1,0)`

). The second matrix b is the transformation matrix that transforms the input data. In our setting, the transformation matrix simply stretches the column vectors.

More precisely, the two column vectors `(1,1)`

and `(1,0)`

are stretched by factor 2 to `(2,2)`

and `(2,0)`

. The resulting matrix is therefore `[[2,2],[2,0]]`

. We access the first row and second column.

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#### Solution

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