### 5.43.13 Modify an element or a row of a matrix : subsop

subsop modifies an element or a row of a matrix. It is used mainly for Maple and MuPAD compatibility. Unlike := or =<, it does not require the matrix to be stored in a variable.
subsop takes two or three arguments, these arguments are permuted in Maple mode.

1. Modify an element
   - In Xcas mode, the first index is 0
     subsop has two (resp. three) arguments: a matrix A and an equality [r,c]=v (resp. a matrix A, a list of indexes [r,c], a value v).
     subsop replaces the element A[r,c] by v.
     Input in Xcas mode :
     subsop([[4,5],[2,6]],[1,0]=3)
     or :
     subsop([[4,5],[2,6]],[1,0],3)
     Output :
     [[4,5],[3,6]]
     Remark
     If the matrix is stored in a variable, for example A:=[[4,5],[2,6]], it is easier to input A[1,0]:=3 which modifies A into the matrix
     [[4,5],[3,6]].
   - In Mupad, TI mode, the first index is 1
     subsop has two (resp. three) arguments: a matrix A and an equality [r,c]=v (resp. a matrix A, a list of index [r,c], a value v).
     subsop replaces the element A[r,c] by v.
     Input in Mupad, TI mode :
     subsop([[4,5],[2,6]],[2,1]=3)
     or :
     subsop([[4,5],[2,6]],[2,1],3)
     Output :
     [[4,5],[3,6]]
     Remark
     If the matrix is stored in a variable, for example A:=[[4,5],[2,6]], it is easier to input A[2,1]:=3 which modifies A into the matrix
     [[4,5],[3,6]].
   - In Maple mode, the arguments are permuted and the first index is 1
     subsop has two arguments: an equality [r,c]=v and a matrix A.
     subsop replaces the element A[r,c] by v.
     Input in Maple mode
     subsop([2,1]=3,[[4,5],[2,6]])
     Output :
     [[4,5],[3,6]]
     Remark
     If the matrix is stored in a variable, for example A:=[[4,5],[2,6]], it is easier to input A[2,1]:=3 which modifies A into the matrix
     [[4,5],[3,6]].
2. Modify a row
   - in Xcas mode, the first index is 0
     subsop takes two arguments : a matrix and an equality (the index of the row to be modified, the = sign and the new row value).
     Input in Xcas mode :
     subsop([[4,5],[2,6]],1=[3,3])
     Output :
     [[4,5],[3,3]]
     Remark
     If the matrix is stored in a variable, for example A:=[[4,5],[2,6]], is is easier to input A[1]:=[3,3] which modifies A into the matrix
     [[4,5],[3,3]].
   - In Mupad, TI mode, the first index is 1
     subsop takes two arguments : a matrix and an equality (the index of the row to be modified, the = sign and the new row value).
     Input in Mupad, TI mode :
     subsop([[4,5],[2,6]],2=[3,3])
     Output :
     [[4,5],[3,3]]
     Remark
     If the matrix is stored in a variable, for example A:=[[4,5],[2,6]], it is easier to input A[2]:=[3,3] which modifies A into the matrix
     [[4,5],[3,3]].
   - in Maple mode, the arguments are permuted and the first index is 1 :
     subsop takes two arguments : an equality (the index of the row to be modified, the = sign and the new row value) and a matrix.
     Input in Maple mode :
     subsop(2=[3,3],[[4,5],[2,6]])
     Output :
     [[4,5],[3,3]]
     Remark
     If the matrix is stored in a variable, for example A:=[[4,5],[2,6]], it is easier to input A[2]:=[3,3] which modifies A into the matrix
     [[4,5],[3,3]].

Remark
Note also that subsop with a ’n=NULL’ argument deletes row number n. In Xcas mode input :

subsop([[4,5],[2,6]],’1=NULL’)

Output :

[[4,5]]