How to generate periodic waveform from amplitude vs time data for a single cycle ?

I have voltage vs time data for a single cycle of a periodic waveform. The voltage is non linear w.r.t. time. How do i generate periodic waveform from this data ?

I have tried by using curve fitting to obtain a linear equation for the data and used y=a*mod(x,T)+c to obtain a periodic waveform. where, y=a*x+c is the curve fitted equation. The code which i used is as follows

t = 10; % total simulation time

T = 3; % period

x = 0:0.1:t;

% lets say your original function is y=2*x which repeated every T second, then y = 2*(mod(x,T));

plot(x,y)

The code gives the periodic waveform but i need to plot it for available nonlinear voltage.