s = rho(T, S )
Calculates density anomally sigma or theta sigma.
This function was called rho and not sigma because there is already a sigma function in Matlab.
Vector of pressure (in dbar).
Vector of temperature or potential temperature (in deg C).
Vector of salinity (in ppm).
Sigma (in kg/m^3) relative to 1000.0 kg/m^3.
Pierre Jaccard, Geophysical Institute, University of Bergen, 1999