Using Riemann sum to calculate approximate integral in R language

definite integral —— The idea of solving the area
in short , Use the sum of small rectangular areas to approximate .

The solution of Riemann integral
This idea is well understood , In short, it is divided into four steps ： Divide first , Then find the area of each rectangle , And then sum up , Finally take the limit .

Let's take Riemann Integrals step by step .

∫ − 4 4 Φ ( x ) ( 1 − Φ ( x ) )   d x \