schmid factor in the single plasticity code of Huang

 Hello

In the code of Prof.Huang, the schmid factor was defined.

For slip deformation tensors

slpdef4=s1m2+s2m1 

slpdef5=s1m3+s3m1

slpdef6=s2m3+s3m2 

For slip spin tensors

slpspn4=(s1m2+s2m1)/2

slpspn5=(s1m3+s3m1)/2

slpspn6=(s2m3+s3m2)/2

 I can't understand the difference of 1/2. Please give me some explanations.

thanks 

wang 

http://www.columbia.edu/~jk2079/fem/umat.html