You have 5 data points and you ve to interpolate the data between them
For plotting in blue cross
plot(ti,yi,'bx','MarkerSize',20,'LineWidth',2)
Now interpolated data and save there result in variable tq and yq
% Your interpolation code
Now plot tq and yq on same graph
hold on
plot(tq,yq,'g--','LineWidth',2)
where tq and yq are your interpolated data