octave:2> odefun=@(t,y) [-2*y(2)*y(1);... > y(1)^2+y(3)^2-y(2)^2-1;... > -2*(y(2)+y(1))*y(3)]; octave:3> help rk23 'rk23' is a function from the file /home/accounts/personale/clrmrc90/aa1819/equazioni_differenziali/rk23.m function [tout,yout] = rk23(odefun,tspan,y0,options) Additional help for built-in functions and operators is available in the online version of the manual. Use the command 'doc ' to search the manual index. Help and information about Octave is also available on the WWW at http://www.octave.org and via the help@octave.org mailing list. octave:4> [tout,yout]=rk23(odefun,[0,15],[0.5,2,10]); octave:5> E=(yout(:,1).^2+yout(:,2).^2+yout(:,3).^2+1)./(2*yout(:,1)); octave:6> size(E) ans = 416 1 octave:7> size(tout) ans = 416 1 octave:8> plot(tout,E,'*') octave:9> options.RelTol=1e-2; octave:10> options.AbsTol=1e-2; octave:11> [tout,yout]=rk23(odefun,[0,15],[0.5,2,10],options); warning: time step rejected warning: time step rejected warning: time step rejected warning: time step rejected warning: time step rejected warning: time step rejected warning: time step rejected warning: time step rejected octave:12> length(tout) ans = 167 octave:13> E=(yout(:,1).^2+yout(:,2).^2+yout(:,3).^2+1)./(2*yout(:,1)); octave:14> length(E) ans = 167 octave:15> plot(tout,E,'*') octave:16> [tout,yout]=rk23(odefun,[0,15],[0.5,2,10],options); octave:17> [tout,yout]=rk23(odefun,[0,15],[0.5,2,10],options); warning: time step rejected warning: time step rejected warning: time step rejected warning: time step rejected warning: time step rejected warning: time step rejected warning: time step rejected warning: time step rejected octave:18> [tout,yout]=rk23(odefun,[0,15],[0.5,2,10],options); octave:19> length(tout) ans = 191 octave:20> plot(tout,yout(:,1)) octave:21> plot(tout,yout(:,2)) octave:22> plot(tout,yout(:,3)) octave:23> plot(tout,yout(:,1)) octave:24> plot(tout,yout(:,2)) octave:25> plot(tout,yout(:,3)) octave:26> diary off