Subscript indices must either be real positive integers or logicals ERROR ,can't solve

This is part of the simple code I'm using:

      for i=1:9
          for v=1:21
              iter=1;
              while dif(i,v)>tol && iter<=maxiter

                  W(i,v)=((v(1+a1(i,v)))^2+(r(i)*omega*(1-a2(i,v)))^2)^0.5;
                  phi(i,v)=atand((v(1+a1(i,v)))/(r(i)*omega*(1-a2(i,v)))); 
                  alpha(i,v)=theta(i)-phi(i,v); 
                  CL(i,v)= -1.692600E-08*(alpha(i,v))^6 + 1.039717E-06*(alpha(i,v))^5 - 7.753536E-06*(alpha(i,v))^4 - 4.279007E-04*(alpha(i,v))^3 + 1.045968E-03*(alpha(i,v))^2 + 1.344549E-01*(alpha(i,v)) + 5.043533E-01; 
                  CD(i,v)= -5.381629E-08*(alpha(i,v))^5 + 2.272123E-06*(alpha(i,v))^4 - 4.127824E-06*(alpha(i,v))^3 + 2.575254E-05*(alpha(i,v))^2 - 4.366098E-04*(alpha(i,v)) + 1.235974E-02; 
                  Tgrad(i,v)=0.5*density*(W(i,v))^2*N*c(i)*(CL(i,v)*cosd(phi(i,v))-CD(i,v)*sind(phi(i,v))); 

                  a1new(i,v)=(-1+(1+Tgrad(i,v)/(pi*density*r(i)*v^2))^0.5)/2;
                  Qgrad(i,v)=0.5*density*(W(i,v))^2*N*c(i)*r(i)*(CL(i,v)*sind(phi(i,v))+CD(i,v)*cosd(phi(i,v))); 
                  a2new(i,v)=Qgrad(i,v)/(4*pi*density*(r(i))^3*v*omega*(1+a1new(i,v)));
                  difa1=abs(a1new(i,v)-a1(i,v));
                  difa2=abs(a2new(i,v)-a2(i,v));

                  if difa1>difa2
                      dif(i,v)=difa1;
                  else
                      dif(i,v)=difa2;
                  end

                  a1(i,v)=a1new(i,v);
                  a2(i,v)=a2new(i,v);
                  iter=iter+1;
             end
          end
      end

The error is: ??? Subscript indices must either be real positive integers or logicals.

Error in ==> flu3try2 at 36 W(i,v)=((v(1+a1(i,v)))^2+(r(i)*omega*(1-a2(i,v)))^2)^0.5;

Why is this happening? I did not have the same error before adding the while loop.

Answer 1

[AC]

Hi,

How did you define your dif function?

The error you get means that at some point you are trying to access part of a vector or a matrix that does not exist, e.g. v(0) or v(0.1).

I would try and debug it and take a look at the values of a1 and a2.

Cheers,

AC

Answer 2

[Jan]

In v(1+a1(i,v)) the index is not a positive integer anymore.

A reliable method to examine such problems:

dbstop if error

Then Matlab stops when the error occurs and you can check the values of the local variables.

[AC]

Hey, now I'm curious: is dif a new name for function diff? When I ran the code, dif was unknown, I assumed it was a user-defined function. Anyway, yes, dbstop is a good friend :)