MATLAB Tutorials class 5: MATLAB inbuild command repmat,repelem,cat,horzcat, and vertcat

MATLAB Tutorials class 5: MATLAB inbuild command repmat,repelem, cat,horzcat, and vertcat


        We discussed MATLAB inbuild command diag,det, and trace in my previous post. We're going to see repmat, repelem, cat,horzcat, and vertcat MATLAB commands and their functions in this post. 

repmat 

repmat command used to repeat the copies of the array. Syntax is

repmat_value=repmat(array,no) 

How to create a matrix in which all elements should be the same in MATLAB?

>> repmat_value=repmat(10,4)

repmat_value =

    10    10    10    10
    10    10    10    10
    10    10    10    10
    10    10    10    10

>> repmat_value=repmat(10,4,3)

repmat_value =

    10    10    10
    10    10    10
    10    10    10
    10    10    10

How to repeat one matrix in square shape and rectangle shape?

>> rand_matrix_creation=randi(2,3)

rand_matrix_creation =

     2     1     1
     1     1     2
     1     2     2

>> repmat_value=repmat(rand_matrix_creation,2,2)

repmat_value =

     2     1     1     2     1     1
     1     1     2     1     1     2
     1     2     2     1     2     2
     2     1     1     2     1     1
     1     1     2     1     1     2
     1     2     2     1     2     2

>> repmat_value=repmat(rand_matrix_creation,2,4)

repmat_value =

     2     1     1     2     1     1     2     1     1     2     1     1
     1     1     2     1     1     2     1     1     2     1     1     2
     1     2     2     1     2     2     1     2     2     1     2     2
     2     1     1     2     1     1     2     1     1     2     1     1
     1     1     2     1     1     2     1     1     2     1     1     2
     1     2     2     1     2     2     1     2     2     1     2     2 

repelem

repmat repeats the whole array but repelem repeats a particular array element. Syntax is

repmat_value=repmat(array,no)

>> rand_matrix_creation=randi(10,1,5)

rand_matrix_creation =

     6     4     2     7     8

In this case, we mentioned 3, so it will repeat each element in 3 times

>> repelem_value=repelem(rand_matrix_creation,3)

repelem_value =

     6     6     6     4     4     4     2     2     2     7     7     7     8     8     8

But in this case, we mentioned 1,3,1,2,1 so it will repeat 6 as 1 one time,4 as 3 times respectively.

>> repelem_value=repelem(rand_matrix_creation,[1,3,1,2,1])

repelem_value =

     6     4     4     4     2     7     7     8

Concatenate (cat)

cat command is used to concatenate array or matrix in MATLAB. Syntax is 

con_array=cat(dim,array1,array2,....arrayN)

How to concatenate array in MATLAB?

>> rand_matrix_creation1=randi(10,3,2)

rand_matrix_creation1 =

     6     6
     5    10
     9     7

>> rand_matrix_creation2=randi(10,3,2)

rand_matrix_creation2 =

    10     3
     3     7
     7     7

If dim=1, it concatenates row-wise(vertically), and if dim=2, it concatenates column-wise(horizontally)
>> con_array=cat(1,rand_matrix_creation1,rand_matrix_creation2)

con_array =

     6     6
     5    10
     9     7
    10     3
     3     7
     7     7

>> con_array=cat(2,rand_matrix_creation1,rand_matrix_creation2)

con_array =

     6     6    10     3
     5    10     3     7
     9     7     7     7

horzcat and vertcat

        horzcat and vertcat command is used to concatenate arrays horizontally and vertically.


>> rand_matrix_creation1=randi(10,3,2)

rand_matrix_creation1 =

     1     7
     3     9
     3     4

>> rand_matrix_creation2=randi(10,3,2)

rand_matrix_creation2 =

     8     7
     7     4
     1    10

>> con_array=horzcat(rand_matrix_creation1,rand_matrix_creation2)

con_array =

     1     7     8     7
     3     9     7     4
     3     4     1    10

>> con_array=vertcat(rand_matrix_creation1,rand_matrix_creation2)

con_array =

     1     7
     3     9
     3     4
     8     7
     7     4
     1    10


and also cat function is used to convert 2 D images to 3 D images. Syntax is 

three_d_im=cat(3,im,im,im) 

we will see this topic detailly in an upcoming post.
 

Reference:


We have discussed the repmat,repelem, cat, horzcat, and vertcat inbuild command in Matlab so far. We will see the next topic in my next post.

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