Usually, the learners from our classes schedule 1-on-1 discussions with the mentors to clarify their doubts. So, thought of sharing the video of one of these 1-on-1 discussions that one of our CloudxLab learner – **Leo** – had **with Sandeep** last week.

Below are the questions from the same discussion.

You can go through the detailed discussion which happened around these questions, in the attached video below.

**Q.1. **In the *Life Cycle of Node Value* chapter, please explain me the below line of code. What are zz_v, z_v and y_v values ?

`zz_v, z_v, y_v = s.run([zz, z, y] `

**Ans.1.** The complete code looks like below:

```
w = tf.constants(3)
x = w + 2
y = x + 5
z = x + 3
zz = tf.square(y+z)
with tf.Session() as s:
zz_v, z_v, y_v = s.run([zz, z, y])
print(zz_y)
```

s.run([zz, z, y]) expression above is basically evaluating zz, z and y, and is returning their evaluated values, which we are storing in variables zz_v, z_v and y_v variables respectively. Basically, the the *run* function of session object returns the same data type as passed in the first argument. Here, the run method is returning an array of values.

TensorFlow is a Python library and in Python, we can return multiple values from a function in the form of a *tuple*. Here is a simple example:

```
x, y , z = [2, 3, 4]
print(x)
2
print(y)
3
print(z)
4
```

Same thing is happening here, s.run() is returning multiple values which are being stored in variables zz_v, z_v and y_v respectively.

So, the evaluated value of zz is stored in variable zz_v, evaluated value of variable z in z_v and evaluated value of variable y in variable y_z.

**Q.2.** In Linear Regression chapter, we are using housing price dataset. How do we know that the model for housing price dataset is a linear equation ? Is it just an assumption ?

**Ans.2.** Yes, it is an assumption that model for housing price dataset is a linear equation.

We can use linear equation for a non-linear problem also.

We convert most of the non-linear problems into a linear problem by using polynomial features.

Even Polynomial Regression problem is solved using Linear Regression by converting a non-linear problem to linear problem by adding polynomial features.

`y = ϴ0 + ϴ1 x + ϴ2 x1 + ϴ3 x2 + ...`

Suppose your equation is

where x1 and x2 are polynomial features and

```
x1 = square(x)
x2 = cube(x)
```

ϴ0, ϴ1, ϴ2, …. etc are weights or also called coefficients.

In Linear Regression, when Gradient Descent is applied on this equation, weights ϴ1 and ϴ3 will go down to 0 (zero) and weight ϴ2 will become bigger. Hence, at the end of Gradient Descent, our above equation will look like below i.e. we get a non-linear equation

```
y = ϴ0 + ϴ2 x1
or , y = ϴ0 + ϴ2 square(x)
```

**Q.3.** Equations of Gradient and Gradient Descent, I don’t understand them

**Ans.3. **

The below equation is for calculating the Gradient

MSE is ‘Mean Squared Error’

m is total number of instances.

X dataset is a matrix with ‘n’ columns (features) and ‘m’ rows (instances).

y is a vector (containing actual values of label) with ‘m’ rows and 1 column

y^ is a also a vector (containing predicted values of label) with ‘m’ rows and 1 column

```
y = ϴ0 + ϴ1 x1 + ϴ2 x2
MSE (E) = square(y∧ - y) / m
MSE (E) = square(ϴ0 + ϴ1 x1 + ϴ2 x2 - y) / m
∂(MSE)/∂ϴ0 = 2(ϴ0 + ϴ1 x1 + ϴ2 x2 - y) / m
= 2/m (X.ϴ - y )
∂(MSE)/∂ϴ1 = 2(ϴ0 + ϴ1 x1 + ϴ2 x2 - y) x1 / m
= 2/m (X.ϴ - y) X
= 2/m X (X.ϴ - y)
```

Therefore, we get,

Below equation is for calculating the Gradient Descent

η is the learning rate here.

ϴ is an array of theta values.

is also an array of values, and is called the *Gradient *or the rate of change of error (E).

If the *Gradient *increases, we need to decrease the ϴ, and if the *Gradient *decreases, we need to increase the ϴ. Eventually, we need to move towards making the *Gradient* equal to 0 (zero) or nearly 0.

**Q.4.** In Gradient Descent, what we can do to avoid getting stuck in *local minima* ?

**Ans.4.** You can use Stochastic Gradient Descent to avoid getting stuck in *local minima*.

You can find more details about this in our Machine Learning course.

For the complete course on Machine Learning, please visit Specialization Course on Machine Learning & Deep Learning