Index exceeds matrix dimensions

I guess this probably the most asked question. I trying to run a for loop which listed below

for i=1:1:288
    if H_tank1(i)<14.5
        if H_tank1(i)>H_limit1
            if H_tank1(i)>H(i) %%%ebb
                H01(i)=H_tank1(i)-H(i);
                Q1(i)=A_inlet*sqrt(2*9.81*H01(i));
                if Q1(i)<150;
                    Q1(i)=Q1(i);
                else
                    Q1(i)=150;
                end
                P1(i)=0.9*9.81*1030*(Q1(i))*H01(i)/1000;

                  if H_tank2(i)<14.5
                      if H_tank2(i)>H_limit2
                          if H_tank2(i)>H_tank1(i)
                              H02(i)=H_tank2(i)-H_tank1(i);
                              Q_ex(i)=A_inlet_ex*sqrt(2*9.81*H02(i));
                              Sum2(i+1)=Sum2(i)-Q_ex(i)*n;
                              H_tank2(i)=Sum2(i)/A_tank2;
                          else
                              H02(i)=H_tank1(i)-H_tank2(i);
                              Q_ex(i)=0;
                              Sum2(i+1)=Sum2(i);
                              H_tank2(i)=Sum2(i)/A_tank2(i);
                          end
                      else
                          if H_tank2(i)>H_tank1(i)
                              H02(i)=H_tank2(i)-H_tank1(i);
                              Q_ex(i)=0;
                              Sum2(i+1)=Sum2(i);
                              H_tank2(i)=Sum2(i)/A_tank2(i);
                          else
                              H02(i)=H_tank1(i)-H_tank2(i);
                              Q_ex(i)=A_inlet_ex*sqrt(2*9.81*H02(i));
                              Sum2(i+1)=Sum2(i)+Q_ex(i)*n;
                              H_tank2(i)=Sum2(i)/A_tank2;
                          end
                      end
                  end

                      Sum1(i+1)=Sum1(i)-(Q1(i)-Q_ex(i))*n;
                      H_tank1(i)=Sum1(i)/A_tank1;

              else
                  H01(i)=-H_tank(i)+H(i);
                  Q1(i)=A_inlet*sqrt(2*9.81*H01(i));
                  if Q1(i)<150;
                      Q1(i)=Q1(i);
                  else
                      Q1(i)=150;
                  end
                  P1(i)=0.9*9.81*1030*(Q1(i))*H01(i)/1000;

                  if H_tank2(i)<14.5
                      if H_tank2(i)>H_limit2
                          if H_tank2(i)>H_tank1(i)

                              H02(i)=H_tank2(i)-H_tank1(i);
                              Q_ex(i)=0;
                              Sum2(i+1)=Sum2(i);
                              H_tank2(i)=Sum2(i)/A_tank2(i);
                          else
                              H02(i)=H_tank1(i)-H_tank2(i);
                               Q_ex(i)=A_inlet_ex*sqrt(2*9.81*H02(i));
                               Sum2(i+1)=Sum2(i)-Q_ex(i)*n;
                               H_tank2(i)=Sum2(i)/A_tank2;
                          end
                      else
                          if H_tank2(i)>H_tank1(i)
                              H02(i)=H_tank2(i)-H_tank1(i);
                              Q_ex(i)=0;
                              Sum2(i+1)=Sum2(i);
                              H_tank2(i)=Sum2(i)/A_tank2(i);
                          else
                              H02(i)=H_tank1(i)-H_tank2(i);
                              Q_ex(i)=A_inlet_ex*sqrt(2*9.81*H02(i));
                              Sum2(i+1)=Sum2(i)+Q_ex(i)*n;
                              H_tank2(i)=Sum2(i)/A_tank2;
                          end
                      end
                  end
                     Sum1(i+1)=Sum1(i)+(Q1(i)-Q_ex(i))*n;
                      H_tank1(i)=Sum1(i)/A_tank1; 

                  end

          end
      end
  end

I have set the starting values for i=1;

H_tank1(1)=13.5;
H_tank2(1)=13.5;
Sum1(1)=H_tank1(1)*A_tank1;
Sum2(1)=H_tank2(1)*A_tank2;

and

H is a vector which has 288 values. Every time I ran the code, I got a message

Index exceeds matrix dimensions.

Error in test (line 22)
    if H_tank1(i)<14.5

and that is for the first loop. which it got stuck. Any suggestion? I don't know why this is happening. Thanks for any helps.

[Geoff Hayes]

Sheng - you say that H is a vector which has 288 values. But is H the same as H_tank1. What are the dimensions of H_tank1?

[sheng deng]

Hi Geoff I want to calculate all the variables based on H, so for each loop, there would be a new H_tank1. like H_tank1(2) would be calculated from H(2) . Thanks

Answer 1

[Geoff Hayes]

sheng - so initially, H_tank1 is a scalar or 1x1 as initialized with

 H_tank1(1)=13.5;

If that is the case, then your code will always succeed on the first iteration of the loop but fail on the second because you have never added any new elements to H_tank1

 if H_tank1(i)<14.5

will always fail for i > 1. Is this really what you want to do? Or do you want to use H instead for this condition?

[sheng deng]

Thanks for your help. I have change the code, I changed H_tank(i) in the calculation for H_tank(i+1). which solved the problem.