Hi, since the exact context of the code isn't clear, I'm making the following assumptions:
- You're probably trying to simulate/animate some form of a crank-slider mechanism.
- You're opening a figure window and plotting these lines continuously. These coordinates are updated in a for loop
- b3 is one point represented as [x,y]. (From the code it looks like it's a weighted average based on lambda)
In this case, your question boils down to representing a single point in a plot window. Now since you're animating, a simple way for you to do this is to use the 'viscircles' command. This will allow you to make an approximate representation of a point with a tiny circle.
With this you can make a visual representation of the ‘point’ by centering a circle on the x,y coordinates for the point (which are stored in b3), with a small radius. The circle will be drawn using the afore-mentioned viscircles command. You will have to choose a radius according to the scale of your animation.
Hope this helps.