The length must be the same
x1 = [0:0.1:1];
f1 = zeros(1,numel(x1)); %f1 with the same length as x1
x2 = [1:0.1:3];
f2 = [1/12*x2.^2 + 1/6*x2 - 1/4]; %change t1 --> x2
x3 = [3:0.1:4];
f3 = ones(1,numel(x3)); %f3 with the same length as x3
figure
plot(x1,f1,x2,f2,x3,f3,'LineWidth',3)
