This function forms the following linear combination of tensors:

Each * represents a scalar multiplication and each + represents naturally a tensor addition.

There is no limit on how many tensors to be summed; that is, N can be any positive integer.

Any of the algebraic c's can be omitted, in which case it is by default substituted by 1.

Simplification:  This routine uses the `tensor/lin_com/simp` routine for simplification purposes.  The simplification routine is applied to each component of result after it is computed.  By default, `tensor/lin_com/simp` is initialized to the `tensor/simp` routine.  It is recommended that the `tensor/lin_com/simp` routine be customized to suit the needs of the particular problem.  It should be noted that `tensor/lin_com/simp` is used frequently as a simplifier by other routines.  See ?tensor[simp] for a list of simplifiers used by each routine of the package.

This function is part of the tensor package, and so can be used in the form lin_com(..) only after performing the command with(tensor) or with(tensor, lin_com).  The function can always be accessed in the long form tensor[lin_com](..).