How do I fix it: Index exceeds matrix dimensions?

Please, I am a begginer on Matlab and when I run my code the following warning appers:

Index exceeds matrix dimensions.

Error in otimizando (line 47) end

-- How can I fix it? I already read that it is because of the size of the matrix, but I can't figure it out. The code is:

i             = 1;

a(i)          = (1+((4*sin(phi_inicial)^2)/solidez*lift_coef*cos(phi_inicial)));

b(i)          = (1-3*a(i))/((4*a(i))-1);

error(i)      = 5; % guess

error1(i)     = 5; % guess

 while (error(i)>=0.00001 || error1(i)>=0.00001)
    phi(i) = tan((1-a(i))/((1+b(i))*lambda_r));
    F = (2/pi)*acos(exp(-((blade_number/2)*(1-(radius_analyzed/radius_total))/((radius_analyzed/radius_total)*sin(phi(i))))));
    alfa(i) = phi(i)*180/pi - beta_inicial;

    lift(i)    = -9e-9*alfa(i)^6 - 3e-7*alfa(i)^5 + 3e-6*alfa(i)^4 - 0.0001*alfa(i)^3 - 0.0003*alfa(i)^2 + 0.1194*alfa(i)+0.0034; % NACA 0012
    drag(i)    = 9e-9*alfa(i)^6 + 2e-8*alfa(i)^5 - 3e-6*alfa(i)^4 -6e-6*alfa(i)^3 + 0.0003*alfa(i)^2 + 0.0003*alfa(i) + 0.0045; % NACA 0012

    trust_coef(i) = (solidez*((1-a(i))^2)*(lift(i)*cos(phi(i))+drag(i)*sin(phi(i))))/sin(phi(i))^2;

    if (trust_coef(i)>= 0.96) % Correção Glauerts
        a(i+1) = (1/F)*(0.143+sqrt(0.0203-0.6427*(0.889-drag(i))));
    else
        a(i+1) = (1+((4*F*sin(phi(i))^2)/(solidez*lift(i)*cos(phi(i)))))^-1;
    end
    b(i+1) = ((4*F*cos(phi(i))/solidez*lift(i))-1)^-1;
    error(i)  = abs(abs(a(i+1))-abs(a(i)));
    error1(i) = abs(abs(b(i+1))-abs(b(i)));
    i      = i + 1;
 end

[Jan]

Please provide the complete error message. Most of all do not let the readers guess, which line is failing.

[João Pedro Cadore]

The message was:

>> otimizando

Index exceeds matrix dimensions.

Error in otimizando (line 46)

end

[James Tursa]

Which line is line 46? And don't use "error" for a variable name, since that is an inbuilt MATLAB function name.

[João Pedro Cadore]

The line 46 is the line of the "end". How I said before, I'm really a beginner on MATLAB. I do not know how to make this loop works. I tried just use a(i+1)-a(i) for my condition in the while loop, but it doesn't work as well.

[João Pedro Cadore]

Now it gave me the following warning:

Attempted to access error(2); index out of bounds because numel(error)=1.

Error in otimizando (line 27)

 while (error(i)>=0.00001 || error1(i)>=0.00001)

Answer 1

[James Tursa]

You don't update the values for error(i+1) and error1(i+1) like you do for a(i+1) and b(i+1), so on the next iteration they are not defined but you attempt to access them. Try this instead:

    error(i+1)  = abs(abs(a(i+1))-abs(a(i)));
    error1(i+1) = abs(abs(b(i+1))-abs(b(i)));

[João Pedro Cadore]

Thank you! You helped me a lot!

[James Tursa]

You're welcome! I would like to note that it took only 6 minutes from the time you posted the actual error message with the offending line for us to figure out the error. The lesson here is, in any future posts you make it will help immensely if you post information like this right up front.