[CIG-LONG] factor in MohrCoulomb

[js at cp.dias.ie]

Hi Walter,
why is there an additional factor term in _MohrCoulomb_GetYieldCriterion?
ie
theta = 0.5 * atan( 1.0 / effectiveFrictionCoefficient);

factor = sin( 2 * theta );

frictionalStrength = effectiveFrictionCoefficient * pressure * factor +
effectiveCohesion * factor;

and don't 2 and 0.5 cancel?

Cheers,

john.