How to solve INDEX OUT OF BOUNDS ERROR? Please help me. Stuck in this for the past 10 days.

eltn=30;             

%%(b)Element Connectivity Table

    count = 0 ;
    conn = zeros([],3) ;
    for i=1:30
        for j=1:27
            count = count+1 ;
        conn(count,:) =[j,j+1,j+2] 
        end
    end
    %Here the Code for Assembling (OR) Global Mass Matrix
    %x(i,j)=Kte_matrix(i,j);                     %DOUBT +=
    for i=1:27
         for j=1:27

          MG_matrix(conn(eltn,i) - 1,conn(eltn,j) - 1)= Mte_matrix(i,j); (ERROR HERE)
         end
    end

How to convert conn matrix in this range??

Attempted to access conn(30,4); index out of bounds because size(conn)=[810,3].

Error in practisee2 (line 558) MG_matrix(conn(eltn,i) - 1,conn(eltn,j) - 1)= Mte_matrix(i,j);

[KSSV]

Obviously you will get error. YOur conn matrix is m*3, it has three columns and you are trying to extract more then three columns from it.

[Virajan Verma]

Yes i know. How to correct this? Is there any way??

[Virajan Verma]

Can RESHAPE command be used here??

[Walter Roberson]

No, there is no way without storing something different in conn.

What are you expecting to retrieve from conn(eltn,i) when i is greater than 3?

[Stephen23]

@Virajan Verma: given that you defined conn to have only three columns, what data do you expect conn(1,27) to contain?

[Virajan Verma]

I simply want a Global mass matrix MG_matrix whose size is 27x27.

[Walter Roberson]

You have not answered the question of what conn(1,27) should evaluate to.

[Virajan Verma]

Actually i dont know the what it would evaluate. I had this C code which i am converting. It reads like this:

for (i = 0; i <27; i++)

  {

    for (j = 0; j <27; j++)

      MG_matrix[con[eltn][i] - 1][con[eltn][j] - 1] += Mte_matrix[i][j];  //2-D array denoted M,N

  }

[Virajan Verma]

for i=1:30
    for j=1:27
        conn(i,j)=58*(j/3)+j+2*i+1
    end
end

[Walter Roberson]

That is quite different initialisation than what you had before.

[Virajan Verma]

That conn matrix is showing index out of bounds error as it has only 3 columns and for i>3, it has no elements to show. That is why i changed the initialization.

Answer 1

[KSSV]

Check the function assemble in the link. This will help you.

https://in.mathworks.com/matlabcentral/fileexchange/32029-plate-bending

[Virajan Verma]

This is to assmble local mass/stiffness matrix to global, but it is nowhere using connectivity matrix.

[KSSV]

It uses......thre are two files..coor.dat and nodes.dat......nodes is the connectivity matrix.

[Virajan Verma]

The assemble function has only this code and there are no such files:

edof = length(index);

for i=1:edof

ii=index(i);

ff(ii)=ff(ii)+f(i);

for j=1:edof

jj=index(j);

kk(ii,jj)=kk(ii,jj)+k(i,j);

end

end

[Virajan Verma]

I got the files. It only contains numerical values and no code is written over there.

[Virajan Verma]

I have changed the conn matrix(which is now a 30x27 matrix) as:

%Connectivity matrix

c1 = 1:2:59 ;

c2 = 2:2:60 ;

c3 = 3:2:61 ;

o = zeros(length(c1),24) ;

conn = [c1' c2' c3' o]

Attempted to access MG_matrix(58,-1); index must be a positive integer or logical.

Error in practisee2 (line 568)

MG_matrix(conn(eltn,i) - 1,conn(eltn,j) - 1)= Mte_matrix(i,j);

How can MG_matrix become -1??

Any suggestions for that??

[Stephen23]

"How can MG_matrix become -1??"

The values of MG_matrix are unrelated to that error message. That error is caused by you trying to use -1 as a index (indices must be positive integers). The error message shows you why it occurs:

Attempted to access MG_matrix(58,-1);  index must be a positive integer or logical.

And where it occurs is pretty easy to figure out:

MG_matrix(conn(eltn,i) - 1,conn(eltn,j) - 1)= Mte_matrix(i,j);
          ^^^^^^^^^^^^^^^^                                       = 58
                           ^^^^^^^^^^^^^^^^                      = -1                  

If conn(eltn,j) is zero, what do you expect conn(eltn,j)-1 to be ?

[Virajan Verma]

The value of conn(eltn,j) for j=1 should be 59. How can it be zero??

[Stephen23]

"The value of conn(eltn,j) for j=1 should be 59. How can it be zero??"

Who said that j is equal to one when that error occurs? I don't see anything in your code that means that j equals one when that error occurs. Try looking at the value of j after the error has occured, and you might just learn something about your code.