Help with error!! attempted to access x(1); index out of bounds because numel(x) =0.

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Trevor 2013-10-1

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https://ww2.mathworks.cn/matlabcentral/answers/88730-help-with-error-attempted-to-access-x-1-index-out-of-bounds-because-numel-x-0

关闭： MATLAB Answer Bot 2021-8-20

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Apologies for the sloppiness

I cannot figure out where I have gone wrong. I am trying to solve a boundary problem using bvp4c.

function project1run
solinit = bvpinit(linspace(3,9,0.2),[-1,1]);
sol = bvp4c(@project1,@project1bc,solinit);
plot (sol.x, sol.y(1,:),'-r')
%part 1 values
%pH = 9
Ckcl = 10
Rp = 40e-9
%if else for values of Ci0
if pH >7
    C10 = 10^(-pH+3);
    C20 = Ckcl+10^(-pH+3)-10^(-(14-pH)+3);
    C30 = Ckcl;
    C40 = 10^(-(14-pH)+3);
else
    C10 = 10^(-pH+3);
    C20 = Ckcl;
    C30 = Ckcl+10^(-pH+3);
    C40 = 10^(-(14-pH)+3);
end
%variables 
epsilonf = 7.08e-10;
F = 96490;
R = 8.31;
T = 300;
z1 = 1;
z2 = 1;
z3 = -1;
z4 = -1;
lambdaD = sqrt(epsilonf*R*T/(F^2*...
    (z1^2*C10+z2^2*C20+z3^2*C30+z4^2*C40)));
r = Rp+5*lambdaD;
%variable for summation 
E = z1^2*C10*exp(-z1*F/(R*T))+z2^2*C20*exp(-z2*F/(R*T))...
    +z3^2*C30*exp(-z3*F/(R*T))+z4^2*C40*exp(-z4*F/(R*T))
%for sigma equation
Ntotal = 1.3285e-5;
Ka = 10^(-7.6+3);
Kb = 10^(-1.9+3);
%phis = 1;
Hs = C10*exp(-F*phis/(R*T));
sigma = -F*Ntotal*((Ka-Kb*Hs^2)/(Ka+Hs+Kb*Hs^2))
%equations for bvp function
function res = project1bc(ya,yb)
pHhigh = 9;
pHlow = 3;
res = [ya(1) yb(2)+sigma/epsilonf]
end
function dydx = project1(x,y)
dphidr = [y(2) 
    -(1/r)*y(2)-((1/epsilonf)*F*E*y(1))]
end
end

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Walter Roberson 2013-10-1

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The only place your code mentions "x" is in

function dydx = project1(x,y)

and then you do not use "x" in the body of that function. Therefor the error must be in something you called from the above code. Please show the complete error message you get, everything that shows up in red when you get the error.

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