The continuous LTI system is

The corresponding discrete system is

What are F and G? Usually we have two methods: use zero-order hold method to discretize it; or use approximation to a rigorous discrete system. Today I will show they are the same to the first order !!! So in the future, we are confident to directly use zero-order holding method to discretize a system as long as you want the first order accuracy!!!

**1) Zero-order holding method:**

where . Then

So

>>>

>>>

**2) Rigorous discrete system**

From

it is easy to see

>>>

>>>

Conclusion: Obviously, method 1 and 2 are equivalent to the first order!!!

Let a be a vector, then , what is ?

If a=[a1,a2,a3]^T, then

[0 -a3 a2]

[a3 0 -a1]

[-a2 a1 0]

You can check it using the definition of cross product, see http://en.wikipedia.org/wiki/Cross_product.

You think you are familiar with homography? No, There are many things you don’t know yet.

See here about point transformation and vector transformation with application in Homography. Note it is easy to be confused when a vector starting from original.

## Are all MLE MVE? At least, MLE of means of Gaussian distribution is MLE. Here is a good note!!! MLE vs MVE

## Multiple classes with the same covariance

If there are multiple classes, each class has many samples. All classes have the same covariance matrix but different mean. So can we use all samples across classes to estimate the covariance matrix? Click here MLE mutiple class, same covariance

See here MLE mean variance!!!