How to integrate using a for loop and plot the result?

Hi, I need to integrate a function using LOOP FOR and plot the result. For example f(x)= cos(x) with 0<=x<=pi. Practically I want to divide the area under the curve in a lot of trapezes, calculate their area and sum them. Can you help me? thank you!!

Answer 1

[Chris Perkins]

Hi Andrea,

You can use "linspace" to create a large number of points over your given range, then calculate the function value at each iteration of the loop, and then calculate the area using the function value and the size of the step. You could plot the area at each step of the loop, or any other values, depending on what exactly you want to plot.

Here's a quick example, using cos(x):

totalArea = 0;
x = linspace(0,pi,10000);
f = zeros(1,length(x));
stepSize = x(2) - x(1);
for i = 1:length(x)
    f(i) = cos(x(i));
    totalArea = totalArea + f(i) * stepSize;
end
disp(totalArea);

Alternatively, if you only need to find the integral, you can use the function "integral", as described on the following documentation page:

https://www.mathworks.com/help/matlab/ref/integral.html

[Andrea Sartori]

Thank you Chris! You've been vey helpful

[Géry van der Rest]

Hi,

Is is possible to do the same procedure, but if the function that I want to integrate is the product of several functions? for example, I want to integrate the function h(x)=(3x^2+x)*(e^3x) by doing a for loop. Can I use the same strategy as the one explained here ?

Thank you very much.