# gsw_rho_first_derivatives_wrt_enthalpy

```partial derivatives of density
with respect to enthalpy (75-term equation)```

## USAGE:

`[rho_SA_wrt_h, rho_h] = gsw_rho_first_derivatives_wrt_enthalpy(SA,CT,p)`

## DESCRIPTION:

```Calculates the following two first-order derivatives of density
(rho),
(1) rho_SA_wrt_h, first-order derivative with respect to Absolute Salinity
at constant h & p.
(2) rho_h, first-order derivative with respect to h at
constant SA & p. ```
```This function uses the computationally-efficient 75-term
expression for specific volume in terms of SA, CT and p (Roquet et al.,
2015).```
```Note that the 75-term equation has been fitted in a restricted range of
parameter space, and is most accurate inside the "oceanographic funnel"
described in McDougall et al. (2003).  The GSW library function
"gsw_infunnel(SA,CT,p)" is avaialble to be used if one wants to test if
some of one's data lies outside this "funnel". ```

## INPUT:

```SA  =  Absolute Salinity                                        [ g/kg ]
CT  =  Conservative Temperature                                [ deg C ]
p   =  sea pressure                                             [ dbar ]
(ie. absolute pressure - 10.1325 dbar)```
```SA & CT need to have the same dimensions.
p may have dimensions 1x1 or Mx1 or 1xN or MxN, where SA & CT are MxN.```

## OUTPUT:

```rho_SA_wrt_h  =  The first derivative of density with respect to
Absolute Salinity at constant CT & p.
[ (kg/m^3)(g/kg)^-1 (J/kg)^-1 ]
rho_h  =  The first derivative of density with respect to
SA and CT at constant p.                 [ (kg/m^3)(J/kg)^-1 ]```

## EXAMPLE:

```SA = [34.7118; 34.8915; 35.0256; 34.8472; 34.7366; 34.7324;]
CT = [28.8099; 28.4392; 22.7862; 10.2262;  6.8272;  4.3236;]
p =  [     10;      50;     125;     250;     600;    1000;]```
`[rho_SA_wrt_h, rho_h] = gsw_rho_first_derivatives_wrt_enthalpy(SA,CT,p)`
`rho_SA_wrt_h =`
```   0.733147960400929
0.733595114830609
0.743886977148835
0.771275693831993
0.777414200397148
0.781030546357425```
`v_h =`
`   1.0e-04 *`
```  -0.831005413475887
-0.826243794873652
-0.721438289309903
-0.445892608094272
-0.377326924646647
-0.334475962698187```

## AUTHOR:

`Paul Barker and Trevor McDougall          [ help@teos-10.org ]`

## VERSION NUMBER:

`3.05 (16th February, 2015)`

## REFERENCES:

```IOC, SCOR and IAPSO, 2010: The international thermodynamic equation of
seawater - 2010: Calculation and use of thermodynamic properties.
Intergovernmental Oceanographic Commission, Manuals and Guides No. 56,
UNESCO (English), 196 pp.  Available from the TEOS-10 web site.```
```McDougall, T.J., D.R. Jackett, D.G. Wright and R. Feistel, 2003:
Accurate and computationally efficient algorithms for potential
temperature and density of seawater.  J. Atmosph. Ocean. Tech., 20,
pp. 730-741.```
```Roquet, F., G. Madec, T.J. McDougall, P.M. Barker, 2015: Accurate
polynomial expressions for the density and specifc volume of seawater
using the TEOS-10 standard. Ocean Modelling.```
`The software is available from http://www.TEOS-10.org`