The purpose of this text is to provide a complete, self-contained
development of the trace formula and theta inversion formula for SL(2,
Z[i])\SL(2, C). Unlike other treatments of the theory, the approach
taken here is to begin with the heat kernel on SL(2, C) associated to
the invariant Laplacian, which is derived using spherical inversion. The
heat kernel on the quotient space SL(2, Z[i])\SL(2, C) is gotten
through periodization, and further expanded in an eigenfunction
expansion. A theta inversion formula is obtained by studying the trace
of the heat kernel. Following the author's previous work, the inversion
formula then leads to zeta functions through the Gauss transform