  Partial trace is a very important mathematical operation in quantum
mechanics. It is not only helpful in studying the subsystems of a composite
quantum system but also used in computing a vast majority of quantum
entanglement measures. Calculating partial trace becomes computationally very
intensive with increasing number of qubits as the Hilbert space dimension
increases exponentially. In this paper we discuss about our new method of
partial tracing which is based on set theory and it is more efficient. The
proposed method of partial tracing overcomes all the limitations of the other
well known methods such as being computationally intensive and being limited to
low dimensional Hilbert spaces. We give a detailed theoretical description of
our method and also provide an explicit example of the computation. The merits
of the new method and other key ideas are discussed.
