@code{simplify_indexed()} will replace all scalar products of indexed
objects that have the symbols @code{A} and @code{B} as base expressions
with the single value 0. The number, type and dimension of the indices
-doesn't matter; @samp{A~mu~nu*B.mu.nu} would also be replaced by 0.
+don't matter; @samp{A~mu~nu*B.mu.nu} would also be replaced by 0.
@cindex @code{expand()}
The example above also illustrates a feature of the @code{expand()} method:
@}
@end example
-The matrix representation of the spinor metric is @code{[[ [[ 0, 1 ]], [[ -1, 0 ]]}.
+The matrix representation of the spinor metric is @code{[[ [[ 0, 1 ]], [[ -1, 0 ]] ]]}.
@cindex @code{epsilon_tensor()}
@cindex @code{lorentz_eps()}
you use the function
@example
-ex dirac_trace(const ex & e, unsigned char rl = 0);
+ex dirac_trace(const ex & e, unsigned char rl = 0, const ex & trONE = 4);
@end example
This function takes the trace of all gammas with the specified representation
-label; gammas with other labels are left standing. The @code{dirac_trace()}
-function is a linear functional that is equal to the usual trace only in
-@math{D = 4} dimensions. In particular, the functional is not cyclic in
-@math{D != 4} dimensions when acting on expressions containing @samp{gamma5},
-so it's not a proper trace. This @samp{gamma5} scheme is described in greater
-detail in @cite{The Role of gamma5 in Dimensional Regularization}.
+label; gammas with other labels are left standing. The last argument to
+@code{dirac_trace()} is the value to be returned for the trace of the unity
+element, which defaults to 4. The @code{dirac_trace()} function is a linear
+functional that is equal to the usual trace only in @math{D = 4} dimensions.
+In particular, the functional is not cyclic in @math{D != 4} dimensions when
+acting on expressions containing @samp{gamma5}, so it's not a proper trace.
+This @samp{gamma5} scheme is described in greater detail in
+@cite{The Role of gamma5 in Dimensional Regularization}.
The value of the trace itself is also usually different in 4 and in
@math{D != 4} dimensions: