I AM GETTING INDEX EXCEEDS MATRIX DIMENSIONS error? PLEASE HELP?

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The following code is used for digital image watermarking using the feature points of the cover image I am getting the following error: Index exceeds matrix dimensions. Error in Algo1 (line 115) M(i1,j1)=a1(i1,j1); Please tell me how to resolve this error code (m file attached for reference)
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Accepted Answer

Walter Roberson
Walter Roberson on 18 Nov 2017
Near line 120, you have
i=1:floor(l/l1);
At that point, l is 64 and l1 is 512, so floor(l/l1) is 0 and i = 1:0 which is empty. Then a small number of lines further down,
for i1=1:l1
for j1=1:m1
temp=i1+(i-1)*l1;
temp1=j1+(j-1)*m1;
M(i1,j1)=a1(temp,temp1);
end
end
with i being empty, temp becomes empty, and a1 gets indexed with the empty vector, giving an empty result. The empty result cannot be stored in the non-empty M(i1,j1)
Now suppose that you had
i=1:floor(l1/l);
giving i=1:512/64 which is i=1:8 . Then with i being a vector, temp=i1+(i-1)*l1 would be a vector, and a1(temp,temp1) would be addressing multiple locations. You cannot store multiple locations in the single location M(i1,j1) either. Therefore that loop is probably wrong.
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More Answers (2)

Jan
Jan on 13 Nov 2017
Start with an auto-indentation to make the code readable: Ctrl-A Ctrl-I. Omit the brute clearing header "clc; close all; clear all;" - there is no reason to clear e.g. all loaded function from the RAM and waste time with reloading from the slow disk.
I cannot run your code due to missing input data and toolboxes.
The code looks strange:
for i1=1:l1
for j1=1:m1
temp=i1+(i-1)*l1;
temp1=j1+(j-1)*m1;
M(i1,j1)=a1(i1,j1);
end
end
What is the reason for overwriting temp and temp1 in each iteration? This would be much simpler:
M = a(1:l1, 1:m1);
But you should get the same error: Obviously a has either less than l1 rows or less than m1 columns. You can find out the details using the debugger:
dbstop if error
Then run the code again. When it stops, check the current values of i1 and j1 as well as the dimension of a1.
The missing comments impede the clarity of the code massively. I would not dare to debug this code or use it.
  1 Comment
Aniket Paranjpe
Aniket Paranjpe on 14 Nov 2017
I Have added a few comments about what the code does, also i have indented the code properly. please go through updated m-file and help me resolve this error

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Aniket Paranjpe
Aniket Paranjpe on 27 Nov 2017
Edited: Walter Roberson on 27 Nov 2017
@Walter Roberson After making the changes you suggested i am getting index exceeds matrix dimensions error at Error in a12 (line 99)
M{i1,j1}=a1(temp,temp1);

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