# bandrv¶

## Purpose¶

Creates a symmetric banded matrix, given its compact form.

## Format¶

y = bandrv(a)
Parameters: a (KxN compact form matrix) – y (KxK symmetric banded matrix) –

## Examples¶

x = { 1 2 0 0,
2 8 1 0,
0 1 5 2,
0 0 2 3 };

// Create a version of 'x' in band format
a = band(x, 1);

// Expand the banded version of 'x' back to a full matrix
y = bandrv(a);


After the code above:

     0   1       1   2   0   0          1   2   0   0
a =  2   8   x = 2   8   1   0      y = 2   8   1   0
1   5       0   1   5   2          0   1   5   2
2   3       0   0   2   3          0   0   2   3


## Remarks¶

a is the compact form of a symmetric banded matrix, as generated by band(). a stores subdiagonals right to left, with the principal diagonal in the rightmost (Nth) column. The upper left corner of a is unused. bandchol() expects a matrix of this form.

y is the fully expanded form of a, a KxK matrix with N-1 subdiagonals.

See also