Index exceeds matrix dimensions.

 if(X(n,5)==X(i(c),5));

[Stephan]

https://de.mathworks.com/matlabcentral/answers/728-how-do-i-write-a-good-question-for-matlab-answers

[KSSV]

You need to show full code.....this error occurs when you try to extract more number of elements then present in the array. Check your dimensions.

[div]

if(X(n,5)==X(i(c),5)); sir can u tell me how to write this code in another way...i m new in matlab

[KSSV]

We cannot help unless the purpose and dimensions of the variables needed. Copy the complete code here.

[div]

for f=1:m
    for i=1:m
         for j=1:4 
             di=abs(X(f,j)-X(i,j));
             Z(i)=di;
         end
         [B,I]=sort(Z);
         for c=1:20

            if(X(f,5)==X(I(c),5)) 
         k=0
  end
  end
  end
  end

[Torsten]

Variable "n" is undefined.

[div]

sorry in place of n there is f

[KSSV]

What is X?

Check this line: X(i(c),5)..your i is a loop variable, it is a scalar....you are trying to access i as a vector in i(c). You need to rethink on this.

[div]

X is a file where data is stored

[div]

how can i solve this sir ...i tried bt no results.

[div]

for f=1:m
    for i=1:m
         for j=1:4 
             di=abs(X(f,j)-X(i,j));
             Z(i)=di;
         end
         [B,I]=sort(Z);
         for c=1:20
            if(X(f,5)==X(I(c),5)) 
         k=0
  end
  end
  end
  end

[Jan]

What does "X is a file" mean? The name of the file?

In the body of the question, there is a lower-case "i", but in the code in the comment an upper-case "I".

Does the code in the comment solve your question?

In

for j=1:4 
  di=abs(X(f,j)-X(i,j));
  Z(i)=di;
end

You overwrite the value of Z(i) 3 times. Afterwards Z(i) contains only the value for j=4.