1. Introduction

Scicos (Scilab Connected Object Simulator) is a Scilab package for modeling and simulation of dynamical systems including both continuous and discrete sub-systems. Scicos includes a graphical editor for constructing models by interconnecting blocks (representing predefined basic functions or user defined functions).

Associated with each signal, in Scicos, is a set of time indices, called activation times, on which the signal can evolve. Outside their activation times, Scicos signals remain constant (see Figure 2). The activation time set is a union of time intervals and isolated points called events.

  

Figure 2: A signal in Scicos and its activation time set.

Signals in Scicos are generated by blocks driven by activation signals. An activation signal causes the block to evaluate its output as a function of its input and internal state. The output signal, which inherits its activation time set from the generating block, can be used to drive other blocks.

Blocks are activated by activation signals which are received on activation input ports placed on top of blocks. A block with no input activation port is permanently active (called time dependent) otherwise it inherits its activation times from the union of activations times of its input signals.

Ports placed at the bottom of blocks are output activation ports. The outgoing signals are activation signals generated by the block. For example, the Clock block generates an activation signal composed of a train of regularly spaced events in time. If this output is connected to the input activation port of a scope block (such as the MScope block), it specifies at what times the value of the inputs of the scope must be displayed.