# INVERSE

## Purpose:

Computes the inverse of a square matrix.

## Syntax:

INVERSE(a)

 a - A square matrix.

A matrix.

## Example:

a = {{1, 3, 4},

{5, 6, 7},

{8, 9, 12}}

b = inverse(a)

b == {{-0.6,     0.0,     0.2},

{ 0.26667, 1.3333, -0.8667},

{ 0.2,    -1.0,     0.6}}

a *^ b == {{1, 0, 0},

{0, 1, 0},

{0, 0, 1}}

to within machine precision.

## Example:

W1: rand(100)

W2: inv(W1)

W3: W1 *^ W2 ## Remarks:

The inverse b of square matrix a produces a result such that:

a *^ b == I, the identity matrix.

The inverse matrix is computed using LU decomposition.

When a is badly scaled or nearly singular, the inverse cannot be obtained. See COND to estimate the condition number and RCOND to estimate the reciprocal condition number.

When det(a) == 0, the matrix is singular and the inverse cannot be calculated reliably. See DET to compute the determinant.

See PINV to compute the pseudo-inverse.

See SVD for an alternate computation of the matrix inverse.

See \^ (Matrix Solve) to efficiently solve a system of equations using LU or QR decomposition.

See LINFIT to fit an arbitrary set of basis functions to a series using the method of least squares.

INVERSE can be abbreviated INV.

See DADiSP/MatrixXL to significantly optimize INVERSE.

*^ (Matrix Multiply)

\^ (Matrix Solve)

COND

DET

LINFIT

LU

MDIV

MMULT

PINV

QR

RCOND

SVD

TRANSPOSE