Learning Objectives for the Lecture:
At the end of the lecture the student is going to be able to:
1. Describe the natural history of heath conditions.
2. Describe the stages of the natural history of heath conditions.
3. Describe the process of prevention.
4. Describe the levels of prevention.
Natural History of Health-related Conditions:
The natural history of health condition is a description of the events that precedes the development of the health condition, and during its occurrence through the course of development, as well as its outcome.

Learning Objectives for the Lecture:
At the end of the lecture the student is going to be able to:
1. Define epidemiology and related concepts.
2. Describe the purpose of epidemiology.
3. List the uses of epidemiology.
4. Identify the term of causality and its related terms.
5. Describe the epidemiological triad and the variations among its elements.
Simple Old Definitions
1. Study the occurrence of illnesses.
2. Branch of medical science which treats epidemics (Oxford English Dictionary).

In the preceding sections we studied parabolas with vertices at the origin and ellipses and
hyperbolas with centers at the origin. We restricted ourselves to these cases because these
equations have the simplest form. In this section we consider conics whose vertices and
centers are not necessarily at the origin, and we determine how this affects their equation 
 

Thyristor is, a three terminal, four layers solid state semiconductor device, each layer consisting of alternately N-type or P-type material, i.e; P-N-P-N.
The conventional thyristor is also known by the name SCR (Silicon Controlled Rectifier).
 They are operated as bistable switches, operating from non conducting state to conducting state.
Thyristors can be assumed as ideal switches for many application, but the practical thyristors exhibit certain characteristics and limitations. 
 

End as a subscript   
To access the last element of a matrix along a given dimension, use  
end as a subscript. This allows you to go to the final element without  
knowing in advance how big the matrix is. For example:  

>> q = 4:10    
q=   
4   5   6   7   8   9   10    

>> q(end)   
ans = 10  

 
>> q(end-4:end)    
ans = 6   7   8   9   10  

 
>> q(end-2:end)   
ans = 8   9   10  

The Colon Operator 
The colon" : " is one of MATLAB’s most important operators. It occurs 
in several different forms. The expression 
>>1:10 
is a row vector containing the integers from 1 to 10 
1 2 3 4 5 6 7 8 9 10 
To obtain nonunit spacing, specify an increment. For example, 
>>100:-7:50 
is 
100 93 86 79 72 65 58 51 
• End as a subscript 
To access the last element of a matrix along a given dimension, use end 
as a subscript. This allows you to go to the final element without knowing 

insert and delete rows and columns:

>> A 
A =

= [1 2 3 ; 4 5 6 ; 7 8 9]

1 2 3 
4 5 6 
7 8 9

>> A(2,2)

an

s

= 5

>> A(3,3)

an

s

= 9 

Lecture2: 
A first steps: 
To get matlab to work out 1 + 1, type the following at the prompt: 
1+1 
matlab responds with 
ans = 2 
The answer to the typed command is given the name ans. In fact ans is 
now a variable that you can use again. For example you can type 
ans*ans 
to check that 2 × 2=4: 
ans*ans 
ans = 4 
Matlab has updated the value of ans to be 4. 
The spacing of operators in formulas does not matter. The following 
formulas both give the same answer: 
1+3 * 2-1 / 2*4 1+3*2-1/2*4