Unit Array

The units and all their components are stored in the unit array. The data type `array' was selected for storing the units, because of its short access time. When the array is filled up by requests from the user interface, the memory management automatically requests a new, bigger array from the operating system. The pointers to the structure components are reallocated, and the old empty array is returned to the operating system.

  
Figure: Internal network data structures (simplified)

Each element of the unit array has the following components:

• Out stores the output value of the unit

• flags contains information for the memory management and the topological type of the unit (see chapter)

• lun the logical unit number

• lln the logical number of the layer the unit belongs to

• *ftype_entry points to the internal representation of the unit type, if a prototype exists for this unit

• Aux saves temporary values needed by internal kernel functions (e.g. backpropagation and topological sort)

• TD saves values needed for time delay networks

• act contains the activation of the unit

• i_act saves the initial activation, used to reset the net

• bias contains the threshold of the unit

• value_a, value_b, value_c general purpose elements for the learning functions

• olddelta, newdelta error values in recurrent networks

• actbuf an array for storage of 10 miscellaneous values

• *out_func points to the output function

• *act_func points to the activation function

• *act_deriv_func points to the derivation function of the activation function

• *act_2_deriv_func points to the second derivation function of the activation function

• *unit_name points to the unit name, a string in the symbol table

• subnet_no contains subnet membership information

• layer_no contains the location of the unit in a multilayer network

• unit_pos stores the position of the unit in the network

• *sites points to a linked structure of input functions or connections

The internal representation of the network is displayed in figure .