## SPRSAX

The SPRSAX function takes a row-indexed sparse array created by the SPRSIN function and multiplies it by an n-element vector to its right.

SPRSAX is based on the routine `sprsax` described in section 2.7 of Numerical Recipes in C: The Art of Scientific Computing (Second Edition), published by Cambridge University Press, and is used by permission.

### Syntax

Result = SPRSAX( A, X [, /DOUBLE] )

### Return Value

Returns a n-element vector.

### Arguments

#### A

A row-indexed sparse array created by the SPRSIN function.

#### X

An n-element right hand vector.

### Keywords

#### DOUBLE

Set this keyword to force the computation to be done in double-precision arithmetic.

### Examples

```; Begin by creating an array A:
A = [[ 5.0,  0.0, 0.0], \$
[ 3.0, -2.0, 0.0], \$
[ 4.0, -1.0, 0.0]]

; Define the right-hand vector:
X = [1.0, 2.0, -1.0]

; Convert to sparse format, then multiply by X:
result = SPRSAX(SPRSIN(A),X)

; Print the result:
PRINT, result
```

IDL prints:

```5.00000     -1.00000      2.00000
```

Introduced: 4.0