Hello, Try to transpose u0.
S. Le 06/04/2020 à 11:41, Cruz a écrit :
Hello everybody, I have a system of 2 differential equations (Eq.1 and Eq.2) coupled of order 2 as shown in the attached image. Normally, I can easily find the solution by transforming this system onto a system of order 1 by changing variables. <https://antispam.utc.fr/proxy/1/c3RlcGhhbmUubW90dGVsZXRAdXRjLmZy/mailinglists.scilab.org/file/t498030/ode.jpg> The variables theta and r are functions of time. I use the ODE solver integrated in Scilab. Here is my code : ------------------------------------------------------------------ t0 = 0; // initial time (s) tmax = 30; // solving max time (s) tinc = 0.005; // time increment (s) t = t0:tinc:tmax; // Differential equations system function du = equadiff(t,u) // d for derivative with respect to time t // u(1) = theta // u(2) = d(theta)/dt // u(3) = r // u(4) = d(r)/dt // du(1) = d(theta)/dt // du(2) = d²(theta)dt² // du(3) = d(r)/dt // du(4) = d²(r)/dt² F1=1300; F2=1000; l=13; k=68000; menv = 112.14; m0 = 56.07; g=9.81; m = (menv - m0) * (1-abs(cos(u(1)))) + m0; du(1) = u(2); du(2) = (F2*sin(u(1)) + (F1-m*g).*cos(u(1)) - 2*m.*u(4).*u(2)) ./ (m.*u(3)); du(3) = u(4); du(4) = ((F1-m*g).*sin(u(1)) - F2*cos(u(1)) - k*(u(3)-l) + m.*u(3).*u(2).*u(2)) ./ m; endfunction // Integration u0 = [0,0,13,0]; [u] = ode(u0,t0,t,equadiff); ------------------------------------------------------------------ The problem is that the output of the solver, [u], should be a matrix of 4 lines and 6001 columns: 4 lines: u (1) = theta u (2) = d (theta) / dt u (3) = r u (4) = d (r) / dt 6001 columns: tmax / tinc = 6000 time step + the initial instant t0 = 6001 At the end of the calculation I get size (u) ans = 1. 24004. instead of 4. 6001. It seems to me to proceed in the standard way for this type of problem. Someone have any idea why it doesn't work? Thanks in advance to all ! -- Sent from: https://antispam.utc.fr/proxy/1/c3RlcGhhbmUubW90dGVsZXRAdXRjLmZy/mailinglists.scilab.org/Scilab-users-Mailing-Lists-Archives-f2602246.html _______________________________________________ users mailing list [email protected] https://antispam.utc.fr/proxy/1/c3RlcGhhbmUubW90dGVsZXRAdXRjLmZy/lists.scilab.org/mailman/listinfo/users
-- Stéphane Mottelet Ingénieur de recherche EA 4297 Transformations Intégrées de la Matière Renouvelable Département Génie des Procédés Industriels Sorbonne Universités - Université de Technologie de Compiègne CS 60319, 60203 Compiègne cedex Tel : +33(0)344234688 http://www.utc.fr/~mottelet _______________________________________________ users mailing list [email protected] http://lists.scilab.org/mailman/listinfo/users
