Staircase signal Time domain Function

Assume you have the following: x1=[0 0.04 0.08 0.12 0.16 0.2 0.24 0.28 0.32 0.36 0.4 0.44 ]; x2=[0 6.25 12.5 18.75 25 31.25 37.5 43.75 50 56.25 62.5 62.5];

figure (1) stairs(x1,x2,'LineWidth',2) xlabel('Time (Sec)') ylabel('Displacement in (V)') grid

I wish to obtain Fourier transform using FFT function in MATLAB. Anyone know how can I describe the staircase waveform in time domain. As the Stairs command in MATLAB only storing figure properties, not the signal as a function of time.