How can I remove linear trend of a regression ?

Hi

To remove linear trend of the curve 'figure (5)', I have used the function detrend but an error was mentioned.

The trend of the curve wanted is attached.

Please help me.

The data used are attached.

The program is

%%

%objet : traitement signal MPF

clc;

clear;

close all;

cd Z:\Matlam\Curves_oscillo_Pc %%

%% load 'data1.txt';

tmp = data1(:,1);

disp = data1(:,2);

acc = data1(:,3);

%on recupère les données Oscilloscope en Volt load 'data4V.txt';

tmpV = data4V(:,1);

Volt = data4V(:,2);

figure(3)

plot(tmpV,Volt,'b',tmpV,Volt,'r.');

xlabel('time (sec)');

ylabel('Voltage(V)');

%%

L=length(tmp)

Lv=length(tmpV)

Fs = 833333333.333; % Sampling frequency

NFFT = 2^nextpow2(L) % Next power of 2 from length of y

NFFTV = 2^nextpow2(Lv) % Next power of 2 from length of y

figure(5)

VOLT = fft(Volt,NFFT)/L; % Calcul de la FFT

amplitude = 2*abs(VOLT(1:NFFT));

f = Fs/4*linspace(0,1,NFFT/2);

semilogy(f(1:NFFT/12),2*abs(VOLT(1:NFFT/12))/(2*abs(ACC(1:NFFT/12))));

y = detrend (abs(VOLT(1:NFFT/12)))

semilogy(f(1:NFFT/12),2*(y))

xlabel('frequency [Hz]')

ylabel('FRF Volatage [V]')