I'm trying to break down a program line by line. `Y`

is a matrix of data but I can't find any concrete data on what `.shape[0]`

does exactly.

```
for i in range(Y.shape[0]):
if Y[i] == -1:
```

This program uses numpy, scipy, matplotlib.pyplot, and cvxopt.

The `shape`

attribute for numpy arrays returns the dimensions of the array. If `Y`

has `n`

rows and `m`

columns, then `Y.shape`

is `(n,m)`

. So `Y.shape[0]`

is `n`

.

```
In [46]: Y = np.arange(12).reshape(3,4)
In [47]: Y
Out[47]:
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11]])
In [48]: Y.shape
Out[48]: (3, 4)
In [49]: Y.shape[0]
Out[49]: 3
```

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