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 January 1st, 2011, 09:52 AM #1 Newbie   Joined: Jan 2011 Posts: 1 Thanks: 0 System of odes, Problem Hello, i would appretiate some help on this... My initial problem is y''=-100y+sin(y), y(0)=0, y'(0)=1, tspan[0,20*pi] and i wanna solve it with Runge-kutta 4 stage,for Xj, j = [0 20], then i ll use this 20 initial values for solving the equations with another method of order 15. I m pasting my code, and i hope someone can figure whats wrong.... xronos = [0 20*pi]; h = (xronos(2)-xronos(1))/n; t_dian=(xronos(1):h:xronos(2))'; x(1) = 0; y(1) = 0; vx(1) = 1; vy(1) = 0; z(1,:)=[x(1) y(1) vx(1) vy(1)]; for j=1:20 initial_buffer(1,:)=z; akrivis_third = feval('methodosbuffer',initial_buffer(j,:),h,t_dia n,j); initial_buffer(j+1,:)=akrivis_third(j,:); end %methodosbuffer function buffer = methodosbuffer(z,h,t_dian,j) b=1; vima=h/6; test(1,:)=z; for a=t_dian(j):vima:t_dian(j+1) testbtonos(b,:)=feval('nonlinear1',test(b,:),t_dia n(j+1)); s1 = testbtonos(b,1:2); s2 = testbtonos(b,1:2) + ((vima/2)* s1); s3 = testbtonos(b,1:2) + ((vima/2)* s2); s4 = testbtonos(b,1:2) + vima * s3; test(b+1,1:2) = test(b,1:2) + (vima/6)* (s1 + 2*s2 + 2*s3 + s4); testbtonos(b,:)=feval('nonlinear1',test(b,:),t_dia n(j+1)); s5 = testbtonos(b,3:4); s6 = testbtonos(b,3:4) + ((vima/2)* s1); s7 = testbtonos(b,3:4) + ((vima/2)* s2); s8 = testbtonos(b,3:4) + vima * s3; test2(b+1,1:2) = test(b,1:2) + (vima/6)* (s5 + 2*s6 + 2*s7 + s8); buffer(j,:) =test(b+1,:); b=b+1; end %nonlinear1 function ztonos =nonlinear1(z,t) y=z(1); yp=z(3); ydp = -100*y + sin(y); ztonos= [yp 0 ydp 0]; Tnx, in advance. Last edited by greg1313; October 12th, 2014 at 06:17 PM. Tags odes, problem, system Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post Execross02 Applied Math 9 July 1st, 2013 08:15 AM eride87 Applied Math 0 March 25th, 2013 07:57 AM singapore Calculus 2 March 19th, 2012 06:48 PM FreaKariDunk Calculus 12 February 22nd, 2012 08:59 PM thetouristbr Calculus 0 March 16th, 2011 05:47 AM

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