function dens=sigmat(t,s);
%function dens=sigmat(t,s);

a1 = ((((6.536332e-9*t - 1.120083e-6).*t ...
     + 1.001685e-4).*t -9.095290e-3).*t...
       + 6.793952e-2).*t + 999.842594;
a2 = (((5.3875e-9.*t + 8.2467e-7).*t + 7.6438e-5).*t ...
     - 4.0899e-3).*t + 8.24493e-1;
a3 = (-1.6546e-6*t + 1.0227e-4).*t - 5.72466e-3;
a4 = 4.8314e-4;
rs = sqrt(abs(s));
dens = (a4*s + a3.*rs +a2).*s + a1 - 1000;


