solve.bdsmatrix {bdsmatrix} R Documentation

## Solve a matrix equation using the generalized Cholesky decompostion

### Description

This function solves the equation Ax=b for x, when A is a block diagonal sparse matrix (an object of class `bdsmatrix`).

### Usage

```## S3 method for class 'bdsmatrix'
solve(a, b, full=TRUE, tolerance=1e-10, ...)
```

### Arguments

 `a` a block diagonal sparse matrix object `b` a numeric vector or matrix, that forms the right-hand side of the equation. `full` if true, return the full inverse matrix; if false return only that portion corresponding to the blocks. This argument is ignored if `b` is present. If the bdsmatrix `a` has a non-sparse portion, i.e., if the `rmat` component is present, then the inverse of `a` will not be block-diagonal sparse. In this case setting full=F returns only a portion of the inverse. The elements that are returned are those of the full inverse, but the off-diagonal elements that are not returned would not have been zero. `tolerance` the tolerance for detecting singularity in the a matrix `...` other arguments are ignored

### Details

The matrix `a` consists of a block diagonal sparse portion with an optional dense border. The inverse of `a`, which is to be computed if `y` is not provided, will have the same block diagonal structure as `a` only if there is no dense border, otherwise the resulting matrix will not be sparse.

However, these matrices may often be very large, and a non sparse version of one of them will require gigabytes of even terabytes of space. For one of the common computations (degrees of freedom in a penalized model) only those elements of the inverse that correspond to the non-zero part of `a` are required; the `full=F` option returns only that portion of the (block diagonal portion of) the inverse matrix.

### Value

if argument `b` is not present, the inverse of `a` is returned, otherwise the solution to matrix equation. The equation is solved using a generalized Cholesky decomposition.

bdsmatrix, gchol

### Examples

```tmat <- bdsmatrix(c(3,2,2,4),
c(22,1,2,21,3,20,19,4,18,17,5,16,15,6,7, 8,14,9,10,13,11,12),
matrix(c(1,0,1,1,0,0,1,1,0,1,0,10,0,
0,1,1,0,1,1,0,1,1,0,1,0,10), ncol=2))
dim(tmat)
solve(tmat, cbind(1:13, rep(1,13)))
```

[Package bdsmatrix version 1.3-4 Index]