How do I calculate velocity with integration from acceleration data?

I am analyzing data from an accelerometer. I first calculated the magnitude and then I inserted a low pass filter. Then I took the integration of the data to get velocity and then again to get displacement. The result I got for my velocity doesn't seem right. There's peaks, but it's at a constant increase which doesn't make sense since the data is 5 consecutive jumps. Here is what I have in my code:

C = table2array(SampleJumpData2); %%Turning table data into matrix
 y1 = SampleJumpData2(:,3); %% matrix and plot for y acceleration
 y = table2array(y1);
 x1 = SampleJumpData2(:,4); %% matrix and plot for x acceleration
 x = table2array(x1);
  z1 = SampleJumpData2(:,2); %% matrix and plot for x acceleration
 z = table2array(z1);
 time=C(:,1);
 
mag = sqrt(sum(x.^2 + y.^2 + z.^2, 2));
 

%%accelerations are integrated twice to produce displacements
 xaccel = plot(time,mag);
xlabel('Time (sec)')
ylabel('Acceleration')
%%Design High Pass Filter
fs = 1000; % Sampling Rate
fc = 0.6;  % Cut off Frequency
order = 2; % 6th Order Filter
%%Filter  Acceleration Signals
[b1 a1] = butter(order,fc,'low');
accxf=filter(b1,a1,mag);
plot(time,accxf,'r'); hold on
plot(time,accxf)
xlabel('Time (sec)')
ylabel('Acceleration')
%%First Integration (Acceleration - Veloicty)
velocity=cumtrapz(time,accxf);
figure (3)
plot(time,velocity)
xlabel('Time (sec)')
ylabel('Velocity')
%%Filter  Veloicty Signals
[b2 a2] = butter(order,fc,'low');
velf = filter(b2,a2,velocity);
%%Second Integration   (Velocity - Displacement)
Displacement=cumtrapz(time, velf);
figure(4)
plot(time,Displacement)
xlabel('Time (sec)')
ylabel('Displacement ')

Answer 1

[madhan ravi]

see https://www.mathworks.com/matlabcentral/answers/275484-integrate-acceleration-to-velocity-and-displacement#answer_215063

velocity=cumtrapz(time,acceleration)

[HN]

What if someone wanted to use Rung Kutta to integrate tabular data of veloocity to get displacement ?

Thanks