IFN Lab: Calibrating IFN

qrCalibratingIFN

By Kardi Teknomo, PhD

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Brief Description

Given the capacity matrix and the known flows at certain links, we can use these link flows to calibrate the parameter of IFN model \( \kappa \) such that the resulting flows at the the known links would be as close as possible to the given link flow. Let \( \mathbf{C} = [c_{ij}] \) be the capacity matrix, \( \kappa \) be the parameter, and \( \mathbf{S} = [s_{ij}] \) be the stochastic matrix. Then, each element \( s_{ij} \) of \( \mathbf{S} \) is given by proportional formula: $$ \mathbf{S} = [s_{ij}] = \frac{c_{ij}}{\sum_{k=1}^{n} c_{ik}} $$ where \( n \) is the number of columns (or rows, since it's a square matrix) in \( \mathbf{C} \). The node vector is computed as $$ \mathbf{\pi} =\begin{bmatrix} \mathbf{S}^{T}-\mathbf{I} \\ \mathbf{j}^{T} \end{bmatrix} \setminus \begin{bmatrix} \mathbf{0} \\ \kappa \end{bmatrix} $$ From the node vector \( \mathbf{\pi} \) and stochastic matrix \( \mathbf{S} \) we can compute the flow matrix with parameter total flow \( \kappa \). $$ \mathbf{F} = \mathbf{\pi} \cdot \mathbf{j}^{T} \circ \mathbf{S} $$ The notation \( \mathbf{x} = \mathbf{K} \setminus \mathbf{b} \) means \( \mathbf{x} = \mathbf{K}^{+} \mathbf{b} \) where \( \mathbf{K}^{+} = (\mathbf{K}^{T}\mathbf{K})^{-1} \mathbf{K}^{T} \) is the Generalized Left Inverse of the Moore Penrose Inverse.

Learning Objectives

Prerequisite

Read: Graph Theory and Linear Algebra

Instruction

  1. Click to generate random capacity matrix. The input capacity matrix must be a non-negative square matrix and irreducible. End each row separated by a semicolon. Separate each data in one row by comma or a space.
  2. Select the link, set the amount of known link flow then click to add this flow into buffer. To delete from buffer, click
  3. Click the arrow in the Lab Tool below to calibrate IFN (right) based on the Capacity matrix (left) and the known link flow in the buffer.
  4. If you modify the capacity matrix directly, click button below to refresh te list of links to be selected for the buffer.

Experiment and Discussion

Lab Tool: Calibrating IFN with known link flows


Capacity matrix




Pattern of Capacity Matrix





Calibrated IFN




Pattern of Ideal Flow Matrix

Ideal Flow Network

IFN Lab: Calibrating IFN

Index