# invhilb

Inverse of Hilbert matrix

## Description

example

H = invhilb(n) generates the exact inverse of the exact Hilbert matrix for n less than about 15. For larger n, the invhilb function generates an approximation to the inverse Hilbert matrix.

H = invhilb(n,classname) returns a matrix of class classname, which can be either 'single' or 'double'.

## Examples

collapse all

Compute the fourth-order inverse Hilbert matrix.

invhilb(4)
ans = 4×4

16        -120         240        -140
-120        1200       -2700        1680
240       -2700        6480       -4200
-140        1680       -4200        2800

## Input Arguments

collapse all

Matrix order, specified as a scalar, nonnegative integer.

Example: invhilb(10)

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical

Matrix class, specified as either 'double' or 'single'.

Example: invhilb(10,'single')

Data Types: char

## Limitations

The exact inverse of the exact Hilbert matrix is a matrix whose elements are large integers. As long as the order of the matrix n is less than 15, these integers can be represented as floating-point numbers without roundoff error.

Comparing invhilb(n) with inv(hilb(n)) involves the effects of two or three sets of roundoff errors:

• Errors caused by representing hilb(n)

• Errors in the matrix inversion process

• Errors, if any, in representing invhilb(n)

The first of these roundoff errors involves representing fractions like 1/3 and 1/5 in floating-point representation and is the most significant.

## References

[1] Forsythe, G. E. and C. B. Moler. Computer Solution of Linear Algebraic Systems. Englewood Cliffs, NJ: Prentice-Hall, 1967.

## Version History

Introduced before R2006a