The Saint Venant-Kirchhoff elastic solid constitutive model.
**Parameters**
- The bulk modulus $`\kappa`$.
- The shear modulus $`\mu`$.
**External variables**
- The deformation gradient $`\mathbf{F}`$.
**Internal variables**
- None.
**Notes**
- The Green-Saint Venant strain measure is given by $`\mathbf{e}=\tfrac{1}{2}(\mathbf{B}-\mathbf{1})`$.