Isotropic class constructor accept others pairs than Young Modulus and Poissons Ratio

[carlos-adir]

A Isotropic instance can have the attributes:

• E Young Modulus
• ν Poissons Ratio
• λ Lamé's first parameter
• μ Lamé's second parameter
• G Shear Modulus
• K Bulk Modulus
• M P-Wave Modulus

In fact, to construct an object, it's only needed two values from these, as shown in Lamé Parameters

Currently, the constructor accepts only the pair (young_modulus, poissons_ratio). It would be nice to add the other combinations.

[carlos-adir]

It's possible by solving the non-linear equations:

$$\lambda + 2G - M = 0$$

$$3\lambda + 2G - 3K = 0$$

$$\lambda \left(E-3G\right)+ G\left(E-2G\right) = 0$$

$$\lambda \left(1-2\nu\right)-2\nu G = 0$$