On Sun, 20 Feb 2005 17:18:09 -0000, "John"
wrote:

Right, ideally you need to multiply I and V and integrate the product.
Easy if you had an 1960's analogue computer, but these are all in museums
now.

There are still plenty in the Burr-Brown or Analogue Devices
catalogues. This is a common enough task and an analogue multiplier is
still an appropriate solution to it.

Given how cheap accurate and stable op-amps have been for years, it's
not that hard to build your own anyway.