##
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. The result is a *
n*
-element vector.

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.

###
Calling Sequence

Result = SPRSAX(*
A, X*
)

###
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.

###
Example

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]]

X = [1.0, 2.0, -1.0]

result = SPRSAX(SPRSIN(A),X)

PRINT, result

IDL prints:

5.00000 -1.00000 2.00000