NCL Home > Documentation > Functions > Spherical harmonic routines

ilapvf

Inverts the vector Laplacian (on a fixed grid) using spherical harmonics.

Prototype

	procedure ilapvf (
		ulap  : numeric,  
		vlap  : numeric,  
		u     : float,    ; or double
		v     : float     ; or double
	)

Arguments

ulap
vlap

the vector Laplacian arrays to invert (input, two or more dimensions, last two dimensions must be nlat x nlon)

input values must be in ascending latitude order
input arrays must be on a global grid

u
v

vector arrays (output, same dimensions as ulap, vlap)

values will be in ascending latitude order
input arrays must be on a global grid

Description

ilapvf inverts the Laplacian vector ulap, vlap and returns the results in the arrays u and v. ilapvf operates on a fixed grid. If the input arrays ulap and vlap are on a gaussian grid, ilapvg should be used.

This procedure does not handle missing values. If any missing values are encountered in a particular 2D input grid, then all of the values in the corresponding output grids will be set to the missing value defined by the output grids' _FillValue attribute.

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

Arrays which have dimensions N 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

Examples

Example 1

Read u and v (on a fixed grid) from a netCDF file and compute the inverse vector Laplacian:

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
begin
   a = addfile("/cgd/cas/shea/MURPHYS/ATMOS/80.fixed.nc","r")
   v200 = a->V(0,{189.},:,:)			; v200 is dimensioned nlat x nlon
   u200 = a->U(0,{189.},:,:)			; u200 is dimensioned nlat x nlon
   printVarSummary(v200)
   ilapl_u = u200			; preallocate space for return array
   ilapl_v = v200			; preallocate space for return array
   ilapvf(u200,v200,ilapl_u,ilapl_v)
end

Errors

If jer or ker is equal to: