Page 459 - ExtendSim User Guide
P. 459

Miscellaneous 433
Biasing flow
Bias order
If a block in a model has bias, it has a bias order that indicates its ranking compared to all the other blocks with bias. Each biasing block is listed in order from the top (strongest) bias order to the lowest (weakest) bias order. The block at the top of the ranking list has a bias order greater than 0. Bias orders lower than the top have numbers higher than the top number; bias numbers that are Blank or less than or equal to 0 are ignored.
Since the bias order is used during the LP calculation of effective rates, changing the bias order often results in a different set of effective rates. It is therefore important to understand the con- cept of bias order and the influence it has on how effective rates are calculated.
☞ The bias of a Bias block is by definition stronger than the biasing effect of any Merge or Diverge block. So Bias blocks will always have higher bias orders than Merge and Diverge blocks.
Bias block
The Bias block allows you to specify a preference for where the flow should be directed. Wherever the Bias block is located in the model, it pulls in as much flow as possible. If a model has multiple Bias blocks, each has its own bias order.
If the model’s Merge and Diverge blocks use non-fixed rules to obtain or distribute flow, there is some leeway in how flow can be biased and the Bias block is useful. If the model’s Merge and Diverge blocks all use fixed rules, there is no possibility of biasing the flow with the Bias block. (Fixed and non-fixed rules are discussed in “Merge and Diverge blocks” on page 434.)
Dialog settings and bias order
The block’s bias order can be set directly in its dialog or it can be modified dynamically through the B (bias) input connector or by linking the Bias order dialog parameter to an ExtendSim data- base. You can enter an initial bias order that has effect until the block gets a bias order value dynamically; you can also show the block’s bias order on its icon.
The Bias dialog shown at the right is for one of two Bias blocks in a model. The block shown has the highest preference for flow, as indicated by the set- ting Bias order: 1.
Bias dialog
The dialog table reports information about each Bias block in the model, its bias order, block label or name, and block number. You can use the table’s Bias column to change the bias order for any of the listed blocks.
Calculation of the effective rate
The preferences for flow defined by Bias blocks has an effect on the calculation of the effec- tive rate. If there is more than one Bias block in the model, each block’s preference is expressed in turn based on its bias order. As each Bias block takes its turn, it calculates the
Discrete Rate


































































































   457   458   459   460   461