# 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 $ *