MATLAB: How to fix it: Index exceeds matrix dimensions

exceeds;matrix;

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

Best Answer

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)));
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