MATLAB: How can i increase the size of * or star in this case

markermarkersizeplot

plot(P(1),P(2),'*r');

i want to increase the size of star(*). how can i ?

sufian - just increase the MarkerSize as

 plot(P(1), P(2), 'r*', 'MarkerSize', 20)

or replace 20 by whatever value makes sense for your plot.

According to the scatter documentation, like this:

scatter(X,Y,20,'k','+')
            ^ this is the size

No, you do not need hold. You can modify the example you find in help polar.