Manipulating Pathway Outputs

It is worthwhile to mention three standard GoldSim elements that are likely to be useful for manipulating pathway outputs:

• Sum element: This element simply adds any specified inputs, producing a single output. Obviously, the inputs must be of the same type and dimension, and the output has the same type and dimension as the inputs. This element can be useful for adding pathway outputs (particularly fluxes or masses). For example, you may wish to compute the total amount of mass in a particular subsystem made up of several pathways, or the total flux rate entering a pathway from several other pathways.

• Extrema element: This element computes the highest or lowest value reached by its input as a function of time, outputting the "peak" or "valley". This can be useful, for example, if you wish to compute the peak concentration, or peak flux rate at a particular location in your system.

• Integrator element: In some cases, you may need to integrate the mass flux leaving a Pathway element using an Integrator. The mass flux leaving a Pathway element represents a rate over the previous timestep. However, Integrators treat their Rate of Change variable as if it is the rate over the next timestep. Hence, when using an Integrator to integrate the mass flux from a Pathway, to account for this difference, you must use the advanced properties the Integrator dialog to adjust how it integrates the Pathway’s output.