Mathematical notations and functions

1. Floor and Ceiling Functions:

If x is a real number, then it means that x lies between two integers which are called the floor and ceiling of x. i.e.

|_x_| is called the floor of x. It is the greatest integer that is not greater than x.
|  x  | is called the ceiling of x. It is the smallest integer that is not less than x.

If x is itself an integer, then |_x_| = | x |, otherwise |_x_| + 1 = | x | E.g.

|_3.14_| = 3, |_-8.5_| = -9, |_7_| = 7

|  3.14  |= 4, |  -8.5  | = -8, |   7   |= 7

2. Remainder Function (Modular Arithmetic):

If k is any integer and M is a positive integer, then:

k (mod M)

gives the integer remainder when k is divided by M.
E.g.

25(mod 7) = 4
25(mod 5) = 0

3. Integer and Absolute Value Functions:

If x is a real number, then integer function INT(x) will convert x into integer and the fractional part is removed.
E.g.

INT (3.14) = 3
INT (-8.5) = -8

The absolute function ABS(x) or | x | gives the absolute value of x i.e. it gives the positive value of x even if x is negative.
E.g.

ABS(-15) = 15 or ABS | -15| = 15
ABS(7) = 7 or ABS | 7 | = 7
ABS(-3.33) = 3.33 or ABS | -3.33 | = 3.33

4. Summation Symbol (Sums):

The symbol which is used to denote summation is a Greek letter Sigma ?.
Let a1, a2, a3, ….. , an be a sequence of numbers. Then the sum a1 + a2 + a3 + ….. + an will be written as:

n
? aj
j=1

where j is called the dummy index or dummy variable.
E.g.

n
? j = 1 + 2 + 3 +…..+ n
j=1

5. Factorial Function:

n! denotes the product of the positive integers from 1 to n. n! is read as ‘n factorial’, i.e.

n! = 1 * 2 * 3 * ….. * (n-2) * (n-1) * n

E.g.

4! = 1 * 2 * 3 * 4 = 24
5! = 5 * 4! = 120

6. Permutations:

Let we have a set of n elements. A permutation of this set means the arrangement of the elements of the set in some order.
E.g.

Suppose the set contains a, b and c. The various permutations of these elements can be: abc, acb, bac, bca, cab, cba.

If there are n elements in the set then there will be n! permutations of those elements. It means if the set has 3 elements then there will be 3! = 1 * 2 * 3 = 6 permutations of the elements.

7. Exponents and Logarithms:

Exponent means how many times a number is multiplied by itself. If m is a positive integer, then:

am = a * a * a * ….. * a (m times)
and
a-m = 1 / am
E.g. 
24 = 2 * 2 * 2 * 2 = 16
2-4 = 1 / 24 = 1 / 16

The concept of logarithms is related to exponents. If b is a positive number, then the logarithm of any positive number x to the base b is written as logbx. It represents the exponent to which b should be raised to get x i.e. y = logbx and by = x
E.g.

  log28 = 3, since 23=8 

log100.001 = - 3, since 10-3
= 0.001
logb1 = 0, since b0
= 1
logbb = 1, since b1
= b

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