lowmat, lowmat1#

Purpose#

Returns the lower portion of a matrix. lowmat() returns the main diagonal and every element below. lowmat1() is the same except it replaces the main diagonal with ones.

Format#

L = lowmat(x)#

L = lowmat1(x)#

Parameters:: x (NxN matrix) – data
Returns:: L (NxN matrix) – containing the lower elements of the matrix. The upper elements are replaced with zeros. lowmat() returns the main diagonal intact. lowmat1() replaces the main diagonal with ones.

Examples#

x = { 1 2 -1,
      2 3 -2,
      1 -2 4 };

L = lowmat(x);
L1 = lowmat1(x);

The resulting matrices are

    1  0  0       1   0   0
L = 2  3  0  L1 = 2   1   0
    1 -2  4       1  -2   1

Remarks#

The lowmat() function along with upmat1() can be used to extract the LU factors from the return.

Source#

diag.src