% Set up initial data for fish2, simulating fish under gravity
     disp('initialize positions and velocities of fish prior to')
     disp('simulating their motion under gravity')
     nfish = input('Input number of fish(10 is reasonable): ');
     zoom = 5;
     rand('seed',0);
     fishp = (rand(nfish,1)-.5) + sqrt(-1)*(rand(nfish,1)-.5);
     fishv = (rand(nfish,1)-.5) + sqrt(-1)*(rand(nfish,1)-.5);
     fishm = ones(nfish,1);
     tfinal = 10.;