When I run my code, I keep getting this error: "Undefined function or variable 'y'."

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Nauryzbay
Nauryzbay el 26 de Mayo de 2023
Comentada: Nauryzbay el 30 de Mayo de 2023
close all;clc
tspan = [0 1];
y0(1)=2;
y0(2)=1;
y0(3)=3;
source = 0;
tol = 1e-3;%Критерии допуска для определения наилучшей стоимости Мой критерий остановки - Tol= 1e-3.
error = 1.0;%Начальная ошибка запуска
while error > tol%ЗАПУСТИТЕ ЦИКЛ WHILE
sol = ode45(@(t,y) ode2(t,y,source), [0 1], y0);% ВЫЗЫВАЕМ СОЛВЕР BVP4C:
t = linspace(0,1,100);
source_new = trapz(t,y(3,:));
error = abs(source_new - source);
source = source_new;
end
figure(1);
subplot(3,1,1)
plot(sol.x,sol.y(1,:),'color','r','Linewidth',1.2);
grid on
hold on
xlabel('\bf t'); ylabel('$$y$$','interpreter','latex','fontsize',16);
subplot(3,1,2)
plot(sol.x,sol.y(2,:),'color','r','Linewidth',1.2);
grid on
hold on
xlabel('\bf t'); ylabel('$$\dot{y}$$','interpreter','latex','fontsize',16);
subplot(3,1,3)
plot(sol.x,sol.y(3,:),'color','r','Linewidth',1.2);
grid on
hold on
xlabel('\bf t'); ylabel('$$y"$$','interpreter','latex','fontsize',16);
function dy = ode2(~,y,source)%y''+y'=1+int^1_0(y'*x)dx;y(0) = 2;y(1) = 4;
m=0.05;
dy = zeros(3,1); % создает нулевой вектор-столбец
dy(1)=y(2);
dy(2)=y(3);
dy(3)=-3/m*y(3)+1/(m.^2)*(1-2*y(2)+4.*source);
end
Undefined function or variable 'y'.
Error in IDTinitial6 (line 14)
source_new = trapz(t,y(3,:));

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Respuesta aceptada

Walter Roberson
Walter Roberson el 26 de Mayo de 2023
Later you keep referring to sol.y so perhaps the reference to y should instead be to sol.y
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Torsten
Torsten el 29 de Mayo de 2023
Editada: Torsten el 29 de Mayo de 2023
... which is y2(1) - y2(0) = y2(1) - 1.
But this also doesn't seem to help - the iteration diverges.
See my symbolic solution and the boundary value solution below.
Nauryzbay
Nauryzbay el 29 de Mayo de 2023
Thank you very much. I'll try to work on it myself.

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Torsten
Torsten el 29 de Mayo de 2023
Editada: Torsten el 29 de Mayo de 2023
Ran in:
syms t y(t)
syms s real
m = 0.05;
Dy = diff(y,t);
D2y = diff(y,t,2);
D3y = diff(y,t,3);
eqn = D3y -( -3/m*D2y + 1/m^2*(1-2*Dy+4*s)) ;
sol_ode = dsolve(eqn)
sol_ode = 
vars = symvar(sol_ode)
vars = 
cond1 = subs(sol_ode,t,0) == 2;
cond2 = subs(diff(sol_ode,t),t,0) == 1;
cond3 = subs(diff(sol_ode,t,2),t,0) == 3;
cond4 = subs(diff(sol_ode,t),t,1) - subs(diff(sol_ode,t),t,0) == s;
sol_cond = solve([cond1,cond2,cond3,cond4])
sol_cond = struct with fields:
C1: 1663/800 C2: -(6*exp(20) + 7*exp(40))/(800*(exp(40) - 4*exp(20) + 2)) C3: (17*exp(40) + 6)/(400*(exp(40) - 4*exp(20) + 2)) s: (10*exp(40) - 23*exp(20) + 13)/(20*(exp(40) - 4*exp(20) + 2))
double(sol_cond.s)
ans = 0.5000
sol_ode = simplify(subs(sol_ode,[vars(1),vars(2),vars(3),vars(4)],[sol_cond.C1,sol_cond.C2,sol_cond.C3,sol_cond.s]))
sol_ode = 
figure(1)
fplot(sol_ode,[0 1])
figure(2)
fplot(diff(sol_ode,t),[0 1])
figure(3)
fplot(diff(sol_ode,t,2),[0 1])
simplify(diff(sol_ode,t,3) -( -3/m*diff(sol_ode,t,2) + 1/m^2*(1-2*diff(sol_ode,t)+4*(subs(diff(sol_ode,t),t,1)-subs(diff(sol_ode,t),t,0)))))
ans = 
0
  2 comentarios
Torsten
Torsten el 29 de Mayo de 2023
Ran in:
A different method to solve the problem:
y0(1)=2;
y0(2)=1;
y0(3)=3;
source = 0.0;
solinit = bvpinit(linspace(0,1,100),y0,source);
sol = bvp4c(@mat4ode, @mat4bc, solinit);
sol = struct with fields:
solver: 'bvp4c' x: [0 0.0101 0.0202 0.0303 0.0404 0.0505 0.0606 0.0707 0.0808 0.0909 0.1010 0.1111 0.1212 0.1313 0.1414 0.1515 0.1616 0.1717 0.1818 0.1919 0.2020 0.2121 0.2222 0.2323 0.2424 0.2525 … ] y: [3×100 double] yp: [3×100 double] parameters: 0.5000 stats: [1×1 struct]
sol.parameters
ans = 0.5000
figure(1)
plot(sol.x,sol.y(1,:))
figure(2)
plot(sol.x,sol.y(2,:))
figure(3)
plot(sol.x,sol.y(3,:))
function dydx = mat4ode(x,y,source) % equation being solved
m = 0.05;
dydx = [y(2);y(3);-3/m*y(3)+1/(m.^2)*(1-2*y(2)+4.*source)];
end
function res = mat4bc(ya,yb,source) % boundary conditions
res = [ya(1)-2.0;ya(2)-1.0;ya(3)-3.0;yb(2)-1.0-source];
end
Nauryzbay
Nauryzbay el 30 de Mayo de 2023
Thank you very much. You've been very helpful.

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