# ilapsf, ilapsg

Invert the Laplacian via Spherepack.

## Synopsis

```    procedure ilapsf(
zlap   : float,
zlmbda : float,
z      : float
)

procedure ilapsg(
zlap   : float,
zlmbda : float,
z      : float
)
```

## Arguments

zlap
The Laplacian array to invert (input, two or more dimensions, last two dimensions must be nlat x nlon and input values must be in ascending latitude order).
zlmbda
If zlap is a two dimensional array then zlmbda may be a constant. If zlap has 3 or more dimensions then zlmbda must be an array with the same dimensions as zlap (minus the rightmost two dimensions). If zlmbda is identically zero, the poisson equation is solved. Otherwise, the Helmholtz equation is solved.
z
the inverted Laplacian array (output, same dimensions as zlap, values will be in ascending latitude order)

## Description

ilapsf and ilapsg both invert the Laplacian zlap and return it in the array z. ilapsf operates on an equal (fixed) grid, and ilapsg operates on a Gaussian grid.

Note: For the arrays whose last two dimensions are nlat x nlon, the rest of the dimensions (if any) are collectively referred to as nt. If the input/output arrays are just two dimensions, then nt can either be considered equal to 1 or nothing at all.

Arrays which have dimensions nt x nlat x nlon should not include the cyclic (wraparound) points when invoking the procedures and functions which use spherical harmonics (Spherepack).

For example, if an array x has dimensions nlat = 64 and nlon = 129, where the "129" represents the cyclic points, then the user should pass the data to the procedure/function via:

```    z = sample ( x([...],:,0:nlon-2) )  ; does not include cyclic points
```

## Error messages

If jer or ker is equal to:
1 : error in the specification of nlat
2 : error in the specification of nlon
4 : error in the specification of nt (jer only)

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\$Revision: 1.8 \$ \$Date: 1999/02/23 15:59:24 \$