Pithoprakta (1955–56) is a piece by Iannis Xenakis for string orchestra (with 46 separate solo parts), two trombones, xylophone, and wood block, premièred by conductor Hermann Scherchen in Munich in March 1957.
The piece is based on the statistical mechanics of gases,[2] Gauss's law,[3] or Brownian motion.
Xenakis drew an analogy between the movement of a gas molecule through space and that of a string instrument through its pitch range.
To construct the seething movement of the piece, he governed the 'molecules' according to a coherent sequence of imaginary temperatures and pressures.
Composer Simon Emmerson notes that this regularity is "impossible in reality and fails to use his ‘stochastic’ approach in this instance.