Added explanations and comments in mattex file

The dislocation based constitutive subroutine can be only use for fcc crystal !!!!
The constitutive equations are different for bcc and hcp.

trunk/mattex.mpie

@@ -14,15 +14,25 @@ s_sat				63
 w0				2.25
 hardening_coefficients        	1.0 1.4
 # Parameters for dislocation-based modeling
+# Initial dislocation density [m]²
 rho0				              1.5e11 
+# Burgers vector [m]                        
 bg			                      2.86e-10
+# Activation energy for dislocation glide [J/K]
 Qedge				              3.0e-19
+# Reference for passing stress [MPa]
 tau0		                              0.0
+# Passing stress adjustment
 c1				              0.1
+# Jump width adjustment
 c2                                            2.0
+# Activation volume adjustment
 c3                                            0.4
+# Dislocation storage adjustment
 c4                      	              0.05
+# Athermal annihilation adjustment
 c5				              10.0
+# Dislocation interaction coefficients
 interaction_coefficients	1.0 2.2 3.0 1.6 3.8 4.5   
 
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