Sunday, September 18, 2011

Numerical Methods: Integration of given function using Trapezoidal rule in C

Source Code:

///integration of given function using Trapezoidal rule
float y(float x){
    return 1/(1+x*x);
int main(){
    float x0,xn,h,s;
    int i,n;
    printf("Enter x0, xn, no. of subintervals: ");
    h = (xn-x0)/n;
    s = y(x0) + y(xn);
    for(i = 1; i < n; i++){
        s += 2*y(x0+i*h);
    printf("Value of integral is %6.4f\n",(h/2)*s);
    return 0;


  1. why %6.4f ?? could you explain this please. Help would be much appreciated, because so far this is the cleanest most nice structured example of the Trapezoidal rule. I need help, because i got an exercise that is about numerical integration.

    Write a C-program which carries out “Numerical Integration” according to (1). Use data
    type double everywhere. “Play” with three different step sizes (b-a) by splitting up the area
    under f(x) into 10, 100 and 1000 trapezoids and compare the results.
    Preferably, use a function for the calculation of (1) and call it from main( ).

    So yeah ;/