# gsw_entropy_first_derivatives

`first derivatives of entropy`

## USAGE:

`[eta_SA, eta_CT] = gsw_entropy_first_derivatives(SA,CT)`

## DESCRIPTION:

```Calculates the following two partial derivatives of specific entropy (eta)
(1) eta_SA, the derivative with respect to Absolute Salinity at
constant Conservative Temperature, and
(2) eta_CT, the derivative with respect to Conservative Temperature at
constant Absolute Salinity.```
 ```Click for a more detailed description of the first derivatives of entropy.```

## INPUT:

```SA  =   Absolute Salinity                                       [ g/kg ]
CT  =   Conservative Temperature                               [ deg C ]```
`SA & CT need to have the same dimensions.`

## OUTPUT:

```eta_SA =  The derivative of specific entropy with respect to
Absolute Salinity (in units of g/kg) at constant Conservative
Temperature.  The eta_SA output has units of:
[ J/(kg K(g/kg))]  or [ J/(g K) ]
eta_CT =  The derivative of specific entropy with respect to
Conservative Temperature at constant Absolute Salinity.
The eta_CT output has units of:                 [ J/(kg K^2) ]```

## 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;]```
`[eta_SA, eta_CT] = gsw_entropy_first_derivatives(SA,CT)`
`eta_SA =`
```  -0.263286800711655
-0.263977276574528
-0.255367497912925
-0.238066586439561
-0.234438260606436
-0.232820684341694```
`eta_CT =`
```  13.221031210083824
13.236911191313675
13.489004628681361
14.086599016583795
14.257729576432077
14.386429945649411```

## AUTHOR:

`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.
See Eqns. (A.12.8) and (P.14a, c) of this TEOS-10 Manual.```
`This software is available from http://www.TEOS-10.org`