deformation gradeint in VUMAT Abaqus Explicit subroutine

Hello everyone,

I'm modelling VUMAT for a composite. So, in my model I have inotropic and anisotropic behaviour. I have modelled isotropic behaviour but for anisotropic behaviour I need to use deformation gradient, which is causing errors. CAN ANYONE HELP with DEFORMATION GRADIENT. How to use that, do we need to rotate stress back in corotational form as abaqus manual says if yes then How?

How can we get Rotation matrix in VUMAT, if we can multiply it with stretch I think we have the result. May be an alternative.....

Please help, stuck badly :(

Thanks in advance