How to plot a cubic spline from the coefficients?

I have a custom function myspline with x and y vector as input, that returns four vectors a,b,c and d that contain the appropiate coefficticients of a cubic spline.

Now I'm supposed to plot the entire spline (in one plot) in a script. The assignment says I should make use of Horner to evaluate the spline functions.

How would I go about doing this? I'm unsure how one would use Horner to get the functions that I need.

[Walter Roberson]

duplicates https://www.mathworks.com/matlabcentral/answers/491168-how-to-plot-a-cubic-spline-from-the-coefficients