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function ADTG = sw_adtg(S,T,P)
% SW_ADTG Adiabatic temperature gradient
%===========================================================================
% SW_ADTG $Revision: 1.4 $ $Date: 1994/10/10 04:16:37 $
% Copyright (C) CSIRO, Phil Morgan 1992.
%
% adtg = sw_adtg(S,T,P)
%
% DESCRIPTION:
% Calculates adiabatic temperature gradient as per UNESCO 1983 routines.
%
% INPUT: (all must have same dimensions)
% S = salinity [psu (PSS-78) ]
% T = temperature [degree C (IPTS-68)]
% P = pressure [db]
% (P may have dims 1x1, mx1, 1xn or mxn for S(mxn) )
%
% OUTPUT:
% ADTG = adiabatic temperature gradient [degree_C/db]
%
% AUTHOR: Phil Morgan 92-04-03 (morgan@ml.csiro.au)
%
% DISCLAIMER:
% This software is provided "as is" without warranty of any kind.
% See the file sw_copy.m for conditions of use and licence.
%
% REFERENCES:
% Fofonoff, P. and Millard, R.C. Jr
% Unesco 1983. Algorithms for computation of fundamental properties of
% seawater. Unesco Tech. Pap. in Mar. Sci., No. 44, 53 pp. Eqn.(31) p.39
%
% Bryden, H. 1973.
% "New Polynomials for thermal expansion, adiabatic temperature gradient
% and potential temperature of sea water."
% DEEP-SEA RES., 1973, Vol20,401-408.
%=========================================================================
%-------------
% CHECK INPUTS
%-------------
if nargin ~= 3
error('sw_adtg.m: Must pass 3 parameters ')
end %if
% CHECK S,T,P dimensions and verify consistent
[ms,ns] = size(S);
[mt,nt] = size(T);
[mp,np] = size(P);
% CHECK THAT S & T HAVE SAME SHAPE
if (ms~=mt) | (ns~=nt)
error('check_stp: S & T must have same dimensions')
end %if
% CHECK OPTIONAL SHAPES FOR P
if mp==1 & np==1 % P is a scalar. Fill to size of S
P = P(1)*ones(ms,ns);
elseif np==ns & mp==1 % P is row vector with same cols as S
P = P( ones(1,ms), : ); % Copy down each column.
elseif mp==ms & np==1 % P is column vector
P = P( :, ones(1,ns) ); % Copy across each row
elseif mp==ms & np==ns % PR is a matrix size(S)
% shape ok
else
error('check_stp: P has wrong dimensions')
end %if
[mp,np] = size(P);
% IF ALL ROW VECTORS ARE PASSED THEN LET US PRESERVE SHAPE ON RETURN.
Transpose = 0;
if mp == 1 % row vector
P = P(:);
T = T(:);
S = S(:);
Transpose = 1;
end %if
%***check_stp
%-------------
% BEGIN
%-------------
a0 = 3.5803E-5;
a1 = +8.5258E-6;
a2 = -6.836E-8;
a3 = 6.6228E-10;
b0 = +1.8932E-6;
b1 = -4.2393E-8;
c0 = +1.8741E-8;
c1 = -6.7795E-10;
c2 = +8.733E-12;
c3 = -5.4481E-14;
d0 = -1.1351E-10;
d1 = 2.7759E-12;
e0 = -4.6206E-13;
e1 = +1.8676E-14;
e2 = -2.1687E-16;
ADTG = a0 + (a1 + (a2 + a3.*T).*T).*T ...
+ (b0 + b1.*T).*(S-35) ...
+ ( (c0 + (c1 + (c2 + c3.*T).*T).*T) + (d0 + d1.*T).*(S-35) ).*P ...
+ ( e0 + (e1 + e2.*T).*T ).*P.*P;
if Transpose
ADTG = ADTG';
end %if
return
%==========================================================================