# Matlab question

## Homework Statement

Write a script file to integrate the function f(x)=x^3+tan(x)+C using the trapezium rule.Calculate the integral between the end points x=2 and x=4 with strip size 0.1.Calculate the integral for range of values from 1 to 3 in steps of 0.1.plot the integral obtained for different values of C?

## Homework Equations

I wrote the code and it is calculating the correct integrals but it is not plotting the integrals obtained for different values of C .can u please help me to modify my code so that it plots :)

## The Attempt at a Solution

This is my code that I have been working on:

% What are the integration limits?
clc
a = 2;
b =4;
% What is the integration step size?
dx = 0.1;
% An array containing the x points.
x = [a:dx:b];
% What is the function to integrate?
C=1:0.1:3;
C;
y =x.^3+tan(x)+C;
% The number of points
N = length(y);
%initialise the area variable
sum_y = 0;
%sum the interior elements of the y array
%note how the loop starts at 2 and stops at N-1
for I = 2:N-1
sum_y = sum_y + y(I);
area = dx*((y(1) + y(N))/2 + sum_y)

plot(area,C)
end

Hi it seems to me that you have find area for different values of C. For every value of C, you have to integrate and find area, this needs outer 'for' loop. To plot the result the variable 'area' should be an array. I have modified your program slightly as given below.

clc
a = 2;
b =4;
% What is the integration step size?
dx = 0.1;
% An array containing the x points.
x = [a:dx:b];
% What is the function to integrate?
for C=1:0.1:3; % This loop to find area for different values of C
y =x.^3+tan(x)+C;
% The number of points
N = length(y);
%initialise the area variable
sum_y = 0;
%sum the interior elements of the y array
%note how the loop starts at 2 and stops at N-1
i=1; % index to store area in an array
for I = 2:N-1
sum_y = sum_y + y(I);
area (i)= dx*((y(1) + y(N))/2 + sum_y); % variable area is an array
i=i+1;
end
plot(area);
hold on % To plot areas for different values of C on same graph
end

Hope this helps

Thank you so much n.karthick :)