Hmm... I can think of two options
1. Use a Divide block, with the "Multiplication" setting to "Matrix". Then, pass the 4-by-4 matrix into a divide port of the Divide block and the V vector in to a multiplication port of the divide block.
2. Use an "MATLAB Function" block (formerly known as the Embedded MATLAB Function block, for pre R2011a users). You could have two inputs - V and the 4-by-4 matrix (A). Then, solve for i with
i = A \ V
To be honest I'm not sure which approach is more efficient numerically (generally, these systems are more accurately solved if you avoid taking the inverse of the matrix and instead solve the system of equations as a whole).
There's a brief description of the matrix behavior of the product block in the "Matrix mode" section here:
Hope this helps!
