upmat, upmat1

Purpose

Returns the upper portion of a matrix. upmat() returns the main diagonal and every element above. upmat1() is the same except it replaces the main diagonal with ones.

Format

u = upmat(x[, k, vector])

u = upmat1(x)

Parameters:

• x (NxK matrix) – data

• k (scalar) – Optional input, an offset for the start of the upper diagonal. See examples.

• vector (scalar) – A binary input with a 1 indicating that the return should be a column vector containing only the upper triangular elements, or a zero indicating the return should be the standard matrix return.

Returns:

u (NxK matrix) – containing the upper elements of x. The lower elements are replaced with zeros. upmat() returns the main diagonal intact. upmat1() replaces the main diagonal with ones.

Examples

Basic example

x = { 7  2 -1,
      2  3 -2,
      4 -2  8 };

u = upmat(x);
u1 = upmat1(x);

The resulting matrices are:

    7  2 -1       1  2 -1
u = 0  3 -2  u1 = 0  1 -2
    0  0  8       0  0  1

Example with offset

Below we will set the second input, k equal to 2. This will set the main diagonal and the diagonal immediately above to be equal to zero.

x = { 16   37   48   46
      19   39   58   85
      84   42   44   63
       8   11   73   50 };


// Set the first 2 bands of the
// upper triangle to zero as well
// as the lower triangle
u = upmat(x, 2);

u =  0    0   48   46
     0    0    0   85
     0    0    0    0
     0    0    0    0

Example with a vector return

Below we will return only the upper triangular elements as a column vector.

x = { 16   37   48   46
      19   39   58   85
      84   42   44   63
       8   11   73   50 };


u = upmat(x, 0, 1);

u = 16
    37
    48
    46
    19
    39
    58
    85
    84
    42
    44
    63
     8
    11
    73
    50

Source

diag.src

See also

Functions lowmat(), lowmat1(), diag(), diagrv(), crout()