In mathematics, we use it as a summation symbol.
In physics, we use its lowercase letter σ to represent the area density. (Therefore, ρ stands for bulk density and η stands for linear density)
Sima writing
mathematical symbol
abstract
Capital σ is used for mathematical summation symbols, such as ∑Pi, where i= 1, 2, ..., t, which is the sum of P 1+P2+ and ...+angle. Lowercase σ is used for statistical standard deviation. Both the с of Cyrillic alphabet and the S of Latin alphabet are derived from Sigma.
It also means summation, which means ∑ j =1+2+3+…+n.
Detailed explanation and application
1, the ∑ symbol means sum, and ∑ is pronounced as sigma, which means sum in English and is the sum.
Examples of ∑ usage
The method of summing with sigma is called Sigma Notation. Its lowercase is σ, which is often used in physics to represent the area density. (Therefore, ρ stands for bulk density and η stands for linear density)
Where I stands for the lower bound, n stands for the upper bound, and k starts from I and goes all the way to n, all of which add up.
∑ i can also be expressed as the sum of I, which is a variable.
3, n can be less than i.
When there is no subscript, it means that the number or symbol is repeated.
For example:
100/ upper limit n
∑ i = 1+2+3+4+5+ + 100
I= 1↘ lower bound I
200
∑ i = 5+6+7+8+9+......+200
i=5
500
∑I = 10+ 1 1+ 12+ 13+ 14+......+500
i= 10
444
∑ Xi = X 1+ X2+ X3+ X4+......+ X444
i= 1
50
∑ i = 1 + 2 + 3 + 4 +......+ 50 = 1275
i= 1
70
∑ iX=X+2X+3X+4X+...+70X=2485X
i= 1
If you know computer programs, this code can help you understand them better. In computer code, it can be expressed as follows:
100
σI = 1+2+3+...+ 100
i= 1
VB:
Dim sum is Double, and n(i is integar) is Double.
Do it while I'm away
Sum = sum +n(i)
i=i+ 1
ring
C++:
# include & ltbits/stdc++。 h & gt
Use namespace std
int n= 100，i= 1，sum = 0； //n indicates the quantity to be added; I indicates where to start adding; Sum stands for cumulative answer.
int main(){
for(； I < = n; ++i){// loop, from i( 1) to n( 100), adding I every time.