Thank you for your respond, but my problem is that my function can be quite complex, it is defined by the user how extensive it can  go and what the period it will hold, then in that case I don't really know hot to manipulate each function element..
Let's say I have the following function...

pforce:=p*sin(omega1*t)+3*cos(3*omega1*t) ;
        here, omega1 is the natural frequency(defined by user), which can yield us the period (T=(2*pi/omega1));
                p any user defined value;
                t time range 
so if the period and function are defined by user, can be any value, then how to plot this function with that period in x-axis 

Thank u