As DavidW points out Out of the box Tcl (like most scripting languages) was never designed for numeric processing. If you want to do numerics and number crunching in Tcl use one of the extensions such as Vectcl or the Mathemtcl. Tcl's C APi makes writing extensions (or wrapping existing libs) pretty straight forward too.

Right - both Python and Tcl/Tk are intended to offload heavy processing to C functions that they stitch together with high level controls.