Accessing and setting parts of a matrix#

Getting and setting a matrix coefficient#

Individual coefficients of a matrix \(A\) are accessed using the A[row,col] syntax. Note that indexing starts at 0, so that the coefficient in the \(4^{\text{th}}\) row and \(2^{\text{nd}}\) column is accessed as A[3,1]. Examples:

>>> from xlcalcnet import *
>>> ctx = mp14.drf()
>>> A = ctx.read_from_sqlite(mp14.dbpath(), "DecTableA6x4", ""); A.show("A")
A:
11,  12,  13,  14,
21,  22,  23,  24,
31,  32,  33,  34,
41,  42,  43,  44,
51,  52,  53,  54,
61,  62,  63,  64,

>>> # gets the coefficient in row number 3 and column number 1
>>> print("A[3,1]: ", A[3,1])
A[3,1]:  42

>>> # sets the coefficient in row number 1 and column number 2 to the value of 99.
>>> A[1,2] = 99; A.show("A")
matA:
11,  12,  13,  14,
21,  22,  99,  24,
31,  32,  33,  34,
41,  42,  43,  44,
51,  52,  53,  54,
61,  62,  63,  64,

Getting and setting a block#

ctx.mat_get_block(matA, i, j, p, q)#

Gets a block of the matrix, starting at row \(i\) and column \(j\), with \(p\) row elements and \(q\) column elements. Writing matA.get_Block(i, j, p, q) has the same effect

>>> from xlcalcnet import *
>>> ctx = mp14.drf()
>>> A = ctx.read_from_sqlite(mp14.dbpath(), "DecTableA6x4", ""); A.show("A")
A:
11,  12,  13,  14,
21,  22,  23,  24,
31,  32,  33,  34,
41,  42,  43,  44,
51,  52,  53,  54,
61,  62,  63,  64,

>>> # gets a block, beginning at A[1, 1], stretching to A[1+3, 1+2]
>>> b1 = A.block(1, 1, 3, 2); b1.show("b1")
b1:
22,  23,
32,  33,
42,  43,

ctx.mat_set_block(matA, i, j, p, q, matB)#

Sets a block of the matrix to matB, starting at row \(i\) and column \(j\), with \(p\) row elements and \(q\) column elements. Writing matA.set_Block(i, j, p, q, matB) has the same effect

>>> # continued from above
>>> # sets b1 into a block, beginning at A[0, 0], stretching to A[0+3, 0+2]
>>> A.set_Block(0, 0, 3, 2, b1); ; A.show("A")
A:
22,  23,  13,  14,
32,  33,  23,  24,
42,  43,  33,  34,
41,  42,  43,  44,
51,  52,  53,  54,
61,  62,  63,  64,

Getting and setting a matrix row#

ctx.mat_get_row(matA, i)#

Gets the \(i^{\text{th}}\) row. Writing matA.get_Row(i) has the same effect

>>> from xlcalcnet import *
>>> ctx = mp14.drf()
>>> A = ctx.read_from_sqlite(mp14.dbpath(), "DecTableA6x4", ""); A.show("A")
A:
11,  12,  13,  14,
21,  22,  23,  24,
31,  32,  33,  34,
41,  42,  43,  44,
51,  52,  53,  54,
61,  62,  63,  64,

>>> # gets row number 2 (i.e. the 3rd row from the top)
>>> r1 = A.row(2); r1.show("r1")
r1:
31,  32,  33,  34,

ctx.mat_set_row(matA, i, matB)#

Sets the \(i^{\text{th}}\) row to matB. Writing matA.set_Row(i, matB) has the same effect

>>> # continued from above
>>> # sets the content of row number 5 to the content of row number 2
>>> A.set_Row(5, A.get_Row(2)); A.show("A")
A:
11,  12,  13,  14,
21,  22,  23,  24,
31,  32,  33,  34,
41,  42,  43,  44,
51,  52,  53,  54,
31,  32,  33,  34,

Getting and setting a matrix column#

ctx.mat_get_col(matA, j)#

Gets the \(j^{\text{th}}\) column. Writing matA.get_Col(j) has the same effect

>>> from xlcalcnet import *
>>> ctx = mp14.drf()
>>> A = ctx.read_from_sqlite(mp14.dbpath(), "DecTableA6x4", ""); A.show("A")
A:
11,  12,  13,  14,
21,  22,  23,  24,
31,  32,  33,  34,
41,  42,  43,  44,
51,  52,  53,  54,
61,  62,  63,  64,

>>> # gets column number 1 (i.e. the 2nd column from the left)
>>> c1 = A.col(1); c1.show("c1")
c1:
12,
22,
32,
42,
52,
62,

ctx.mat_set_col(matA, j, matB)#

Sets the \(j^{\text{th}}\) column to matB. Writing matA.set_Col(j, matB) has the same effect

>>> # continued from above
>>> # sets the content of column number 3 to the content of column number 1
>>> A.set_Col(3, A.get_Col(1)); A.show("A")
A:
11,  12,  13,  12,
21,  22,  23,  22,
31,  32,  33,  32,
41,  42,  43,  42,
51,  52,  53,  52,
61,  62,  63,  62,

Getting and setting a diagonal#

ctx.mat_get_diagonal(matA, q=0)#

Gets the diagonal or a subdiagonal of the matrix. Writing matA.get_Diagonal(q=0) has the same effect.

>>> from xlcalcnet import *
>>> ctx = mp14.drf()
>>> A = ctx.read_from_sqlite(mp14.dbpath(), "DecTableA6x4", ""); A.show("A")
A:
11,  12,  13,  14,
21,  22,  23,  24,
31,  32,  33,  34,
41,  42,  43,  44,
51,  52,  53,  54,
61,  62,  63,  64,

>>> # gets the first lower subdiagonal
>>> b1 = A.diagonal(-1); b1.show("b1")
b1 = A.diagonal(-1):
21,
32,
43,
54,

ctx.mat_set_diagonal(matA, q, matB)#

Sets the diagonal or a subdiagonal of the matrix to matB. Writing matA.set_Diagonal(q, matB) has the same effect.

>>> # continued from above
>>> # sets the diagonal to the first lower subdiagonal
>>> A.set_Diagonal(0, b1); A.show("A")
A:
21,  12,  13,  14,
21,  32,  23,  24,
31,  32,  43,  34,
41,  42,  43,  54,
51,  52,  53,  54,
61,  62,  63,  64,

Getting and setting a triangular view#

ctx.mat_get_triangular_view(matA, view=1)#

Gets the triangular view of the matrix. Writing matA.get_TriangularView(View = 1) has the same effect.

>>> from xlcalcnet import *
>>> ctx = mp14.drf()
>>> A = ctx.read_from_sqlite(mp14.dbpath(), "DecTableA6x4", ""); A.show("A")
A:
11,  12,  13,  14,
21,  22,  23,  24,
31,  32,  33,  34,
41,  42,  43,  44,
51,  52,  53,  54,
61,  62,  63,  64,

>>> # gets the first lower subdiagonal
>>> b1 = A.diagonal(-1); b1.show("b1")
b1 = A.diagonal(-1):
21,
32,
43,
54,

ctx.mat_set_triangular_view(matA, view, matB)#

Sets the triangular view of the matrix to matB. Writing matA.set_TriangularView(View, matB) has the same effect.

>>> # continued from above
>>> # sets the diagonal to the first lower subdiagonal
>>> A.set_Diagonal(0, b1); A.show("A")
A:
21,  12,  13,  14,
21,  32,  23,  24,
31,  32,  43,  34,
41,  42,  43,  54,
51,  52,  53,  54,
61,  62,  63,  64,

Accessing and setting parts of a matrix

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