Cartesian, cylindrical, and spherical coordinates

in which tension is positive.

Newton's law of viscosity: Tau=+mu dv/dx

This file uses the stress sign convention from Bird et al. and Morrison, Understanding Rheology 2001

in which compression is positive

Newton's law of viscosity: Tau=-mu dv/dx

Note: the difference only affects

xpressions with tau or Pi;

the Navier-Stokes and the Continuity equation

are not affected (stress does not appear).

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