Asked by Sumedh Kulkarni
on 26 Jan 2018

The aim is to create a matrix (C_n) from two different matrices (M) and (t_e1) using a equality condition. I am trying to use the following code to do this. However,it gives me output as a matrix with zeros.

C_n=zeros(length(M),length(int));

for i= 1:length(int) %%length(int)=96

for j=1:length(M) %%length(M)=300

if M(j,i)==t_e1(j,1) %%t_e1 is of size 300*2 and M is 300*96

C_n(j,i)=t_e1(j,2); %%Want to check each element of M that equals (j,1)th element of t_e1

%%if true, replace each element of C_n by (j,2)th element of t_e1

end

end

end

What am I doing wrong in the above code?? Also, is there a better way to do get the required output (not using loops)?

Thank you!

Answer by Youssef Khmou
on 26 Jan 2018

Edited by Walter Roberson
on 26 Jan 2018

By computing the difference between the two matrices A and B, find the indexes of the entries that equal zero and replace the entries of matrix C with the inputs of the indexes:

example:

A=round(100*rand(4));

B=round(100*rand(4));

T=A-B;

C=zeros(size(A));

[a,b]=find(T==0);

C(a,b)=A(a,b);

Sumedh Kulkarni
on 26 Jan 2018

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Answer by Domanic
on 26 Jan 2018

Edited by Domanic
on 26 Jan 2018

I think the original code you had was correct, Sumedh. A minimum working example would be helpful, though. Try the following, which computes your loops on one line using logical vectors.

%%Set up example matrices

int = randi([0 3],[96 1]);

M=randi([0 3],[300 96]);

t_e1 = randi([0 3],[300, 2]);

%%Compute C_n

C_n = t_e1(:,2).*(M==t_e1(:,1));

Sumedh Kulkarni
on 1 Feb 2018

Dominac, this doesnt work either. I tried to use the example you provided, which works quite well. But for me, i think the elements of Matrix M have same values in some columns. Maybe that`s the reason? It looks something like this:

9 12 20 20 39

10 13 23 36 94

12 20 36 39 124

13 23 39 49 200

20 36 49 94 226

23 39 57 106 275

24 49 94 110 0

36 57 106 124 0

37 88 110 137 0

39 94 124 200 0

49 102 137 201 0

57 106 141 226 0

63 110 200 275 0

75 114 201 0 0

and t_e1 looks like this:

1 92

2 91

3 29

4 93

5 92

6 28

7 68

8 93

9 95

10 96

11 52

12 96

13 96

14 82

15 85

Basically, M(1,1) is t_e1(9,1) and I want element corresponding to t_e(9,1), which is t_e1(9,2) in the new matrix. This needs to be done for each element in matrix M.

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