Problem about the Jacobian matrix (DDSDDE) in UMAT

Hi all friends,

I have a basic question. Why the Jacobian matrix (DDSDDE) in UMAT is defined as:

∂Δσ/∂Δε

rather than:

 ∂σ/∂ε

And what's the difference between them

Thank you all for your help,

Tianhao Yan