Imaginary part arises when the data imported from excel sheet is double integrate

Hi I double integrated two columns of data in excel sheet but in the output the displaced data has imaginary part can some one help me to avoid the imaginary part. clear; clc; w = xlsread('Book3.xlsx'); dt=.02; t=[0:dt:20]; disp = discrt(w,dt); plot(t,disp,'r',t,w); xlabel('Time') ylabel('displacement') title('Integrated unfiltered plot') %legend ('X integrated displacement')