2.12.1 Indexing in matrices

Indexing in matrices can be done by giving the indices of selected rows and columns or by boolean indices or by using the $ symbol.

 
-->A=[1 2 3;4 5 6]
 A  =
 
!   1.    2.    3. !
!   4.    5.    6. !
 
-->A(1,2)
 ans  =
 
    2.  
 
-->A([1 1],2)
 ans  =
 
!   2. !
!   2. !
 
-->A(:,1)
 ans  =
 
!   1. !
!   4. !
 
-->A(:,3:-1:1)
 ans  =
 
!   3.    2.    1. !
!   6.    5.    4. !
 
-->A(1)
 ans  =
 
    1.  
 
-->A(6)
 ans  =
 
    6.  
 
-->A(:)
 ans  =
 
!   1. !
!   4. !
!   2. !
!   5. !
!   3. !
!   6. !
 
-->A([%t %f %f %t])
 ans  =
 
!   1. !
!   5. !
 
-->A([%t %f],[2 3])
 ans  =
 
!   2.    3. !
 
-->A(1:2,$-1)
 ans  =
 
!   2. !
!   5. !
 
-->A($:-1:1,2)
 ans  =
 
!   5. !
!   2. !
 
-->A($)
 ans  =
 
    6.  
 
-->//
 
-->x='test'
 x  =
 
 test   
 
-->x([1 1;1 1;1 1])
 ans  =
 
!test  test  !
!            !
!test  test  !
!            !
!test  test  !
 
-->//
 
-->B=[1/%s,(%s+1)/(%s-1)]
 B  =
 
!   1     1 + s  !
!   -     -----  !
!   s   - 1 + s  !
 
-->B(1,1)
 ans  =
 
    1   
    -   
    s   
 
-->B(1,$)
 ans  =
 
    1 + s   
    -----   
  - 1 + s   
 
-->B(2) // the numerator
 ans  =
 
!   1     1 + s  !
 
-->//
 
-->A=[1 2 3;4 5 6]
 A  =
 
!   1.    2.    3. !
!   4.    5.    6. !
 
-->A(1,2)=10
 A  =
 
!   1.    10.    3. !
!   4.    5.     6. !
 
-->A([1 1],2)=[-1;-2]
 A  =
 
!   1.  - 2.    3. !
!   4.    5.    6. !
 
-->A(:,1)=[8;5]
 A  =
 
!   8.  - 2.    3. !
!   5.    5.    6. !
 
-->A(1,3:-1:1)=[77 44 99]
 A  =
 
!   99.    44.    77. !
!   5.     5.     6.  !
 
-->A(1,:)=10
 A  =
 
!   10.    10.    10. !
!   5.     5.     6.  !
 
-->A(1)=%s
 A  =
 
!   s     10     10  !
!                    !
!   5     5      6   !
 
-->A(6)=%s+1
 A  =
 
!   s     10     10     !
!                       !
!   5     5      1 + s  !
 
-->A(:)=1:6
 A  =
 
!   1.    3.    5. !
!   2.    4.    6. !
 
-->A([%t %f],1)=33
 A  =
 
!   33.    3.    5. !
!   2.     4.    6. !
 
-->A(1:2,$-1)=[2;4]
 A  =
 
!   33.    2.    5. !
!   2.     4.    6. !
 
-->A($:-1:1,1)=[8;7]
 A  =
 
!   7.    2.    5. !
!   8.    4.    6. !
 
-->A($)=123
 A  =
 
!   7.    2.    5.   !
!   8.    4.    123. !
 
-->//
 
-->x='test'
 x  =
 
 test   
 
-->x([4 5])=['4','5']
 x  =
 
!test        4  5  !