Index in position 1 exceeds array bounds (must not exceed 6). Matrix is singular, close to singular or badly scaled. Results may be inaccurate. RCOND = NaN.

Please help debug. I marked the lines that outputs error.

It gives complex double when I debug it.

This is another version of the code. Any help is appreciated. Thanks!

p_o(n+1,:)=A\R; %%% this one gives warning %%%%

for i = 1:10
    if i == 1
      
        qt(n,i)=injection_rate;
        
        Twr=2.6366^10-4*permeability*lamda_w(n,i)*(dydz/delta_x);
        
        S_w(n+1,i)=(1+(rock_compressibility+water_compressibility)*(p_o(n+1,i)-p_o(n,i)))*S_w(n,i)+(delta_time/(VR*porosity))*(Twr*(p_o(n+1,i+1)-p_o(n+1,i))-Twr*(p_cow(n,i+1)-p_cow(n,i))+qt(n,i));
        
    else
        qt(n,i)=-WI(n,i)*(p_o(n,i)-p_well);
        Twl=Twr;
        
        Twr=2.6366*10^-4*permeability*lamda_w(n,i)*(dydz/delta_x);
        
        S_w(n+1,i)=(1+(rock_compressibility+water_compressibility)*(p_o(n+1,i)-p_o(n,i)))*S_w(n,i)+(delta_time/(VR*porosity))*(Twr*(p_o(n+1,i+1)-p_o(n+1,i))-Twl*(p_o(n+1,i)-p_o(n+1,i-1))-Twr*(p_cow(n,i+1)-p_cow(n,i))+Twl*(p_cow(n,i)-p_cow(n,i-1)));
  
    end
    
    if S_w(n+1,i)<S_wr
        S_w(n+1,i)=S_wr;
    end
       

[KSSV]

Same question https://in.mathworks.com/matlabcentral/answers/447644-i-am-getting-this-error-and-do-not-know-how-to-fixt-it-warning-matrix-is-singular-close-to-singu

Answer 1

[Sven]

You wrote

2.6366^10-4

instead of

2.6366*10^-4 

You could also write it like this

2.6366e-4

This solved any errors and warnings. Here in this line:

p_o(n+1,:)=A\R; %%% this one gives warning %%%%
for i = 1:10
    if i == 1
      
        qt(n,i)=injection_rate;
        
        % Before: Twr=2.6366^10-4*permeability*lamda_w(n,i)*(dydz/delta_x);
        Twr=2.6366e-4*permeability*lamda_w(n,i)*(dydz/delta_x);