docs: def calc_equivalent_modulus(self):
          """Calculates the equivalent laminate properties.
  
          The following attributes are calculated:
              e1, e2, g12, nu12, nu21
  
          """
          AI = np.matrix(self.ABD, dtype=np.float64).I
          a11, a12, a22, a33 = AI[0,0], AI[0,1], AI[1,1], AI[2,2]
          self.e1 = 1./(self.h*a11)
          self.e2 = 1./(self.h*a22)
          self.g12 = 1./(self.h*a33)
          self.nu12 = - a12 / a11
          self.nu21 = - a12 / a22