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matlabfunctionplotintintegral

How to do a indefinite integral of a vector and plot it

I'm new to Matlab and wanted to integrate a section-wise integrated vector.

The code I use to create a vector looks like this:

dt=1/1000;
t=0:dt:6;

g(t<=0)=0;
g(t>=0 & t<=1)=1*t(t>=0 & t<=1);
g(t>=1 & t<=3)=1;
g(t>=3 & t<=4)=-1*(t(t>=3 & t<=4)-4);
g(t>=4)=0;

I managed to get it work with a diff() operation:

function [h] = diff_plot(g,t)

dt = 1/1000;

h = diff(g)*1/dt;
h(end) = h(end-1);

subplot(2,1,1);
plot(t,g);
grid on;
xlabel('Zeit in T');
title('g(t)');

subplot(2,1,2);
plot(t,h);
grid on;
xlabel('Zeit in T');
title('h(t)=dg(t)/dt');

end

But now i don't know how to do it with the int() - function. I always get the error "Undefined function 'int' for input arguments of type 'double'."

Solution

  • You could use cumsum in an oposite way of diff function.

    Below is description of cumsum function.

    B = cumsum(A) returns the cumulative sum of A starting at the beginning of the first array dimension in A whose size does not equal 1.

    By multiplying dt, you can calculate integral of discrete function.

    int_g=cumsum(g)*dt;

plot(t,int_g)