Index exceeds array bounds in BVP problem

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Gleb
Gleb 2021-1-17
评论： Gleb 2021-1-20
I'm trying to make FEM for my boundary value problem. matlab gives an error "Index exceeds array bounds.
Error in Gas_system_4>fun (line 28)
Y_gHMX= Y_gHMX_(i);
"
I assume its because i use element of vector Y_gHMX_ outside of the loop. But how to fix it
function Gas_system_4
clc
close all
n = 100;
x0 = ones(2*n,1);
sol = fsolve(@(x)fun(x,n),x0);
norm(fun(sol,n))
x = ((1:n)-1)/(n-1);
plot(x,sol(1:n))
end
function res = fun(Yg,n)
% some initial and boundary conditions and constanta
% ...
% ...
x = ((1:n)-1)/(n-1);
dx = 1/(n-1);
T_g_ = Yg(1:n);
Y_gHMX_ = Yg(n+1:2*n);
for i=1:n
T_g= T_g_(i);
end
for i=n+1:2*n
Y_gHMX= Y_gHMX_(i);
end
% some functions of T_g and Y_gHMX
Pe_g=...
Pe_dk = ..
w_gHMX=...
Q_react_g=...
res_T_g_ = zeros(n,1);
res_Y_gHMX_ = zeros(n,1);
res_T_g_(1) = T_g_(1)-T_fout;
for i=2:n-1
res_T_g_(i) = (1./Pe_g).*(T_g_(i+1)-2*T_g_(i)+T_g_(i-1))/dx^2 - (T_g_(i+1)-T_g_(i-1))/(2*dx) + Q_react_g;
end
res_T_g(n) = T_g_(n);
res_Y_gHMX_(1) = Y_gHMXout(1);
for i = 2:n-1
res_Y_gHMX_(i) = (1./Pe_dk)*(Y_gHMX_(i+1)-2*Y_gHMX_(i)+Y_gHMX_(i-1))/dx^2-(Y_gHMX_(i+1)-Y_gHMX_(i-1))/(2*dx) +w_gHMX;
end
res_Y_gHMX(n) = Y_gHMX_(n)-0;
res = [res_T_g;res_Y_gHMX];
end

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采纳的回答

Cris LaPierre
Cris LaPierre 2021-1-18
编辑：Cris LaPierre 2021-1-18
Because i exceeds the length of Y_gHMX.
I see your index relates to the values you extracted from Y_gHMX_. However, once extracted, the index of Y_gHMX starts at 1, not n+1, and ends at (2*n-(n+1)+1). You could just use length(Y_gHMX) instead.

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