Visualization of Flux Analysis results: a) The results of the flux calculation for Saccharomyces cerevisiae are illustrated. The flux values were obtained through least squares, since the configured system was determined. The thickness of the arrows is proportional to the flux value of the corresponding reactions, after overlaying the fluxes over the network layout. Thin light grey arrows represent reactions with no flux value. b) The central carbon metabolism of Escherichia coli is shown with a comparison between pFBA-based simulations before and after adding metabolic flux ratio constraints. Here, grey arrows indicate reactions where there is no flux in both simulations, while red and green arrows represent reactions for which the simulations with and without flux ratios, respectively, returned flux values. The darker the arrows are, the nearer the fluxes in both simulations.