ECE- Lab 4: A Resistor Network Simulator Solution

Description

• Objectives

This assignment will give you practice in creating and manipulating linked lists in C++. You will also see how to programs can be used to simulate hardware circuitry.

• Problem Statement

The lab builds on Lab 3, but adds several new features.

You will replace arrays with linked lists to eliminate the maximum-size limitations of the previous program, and to allow you to implement the delete resistor command.

You will add a new solve capability to the program so that it can nd the dc voltage at each node.

• Preparation & Background

This lab builds on the previous lab in its use of classes, constructors, and member functions. You should review the textbook and lecture notes pertaining to the following topics:

Constructors and destructors

Class member variables and functions Public/private access types

Dynamic memory management with new and delete Linked lists

• Speci cations

The program shall build on the program you developed in Lab 3, with the most sigini cant mod-i cations summarized in the following list. Detail is given in the appropriate subparts of Sec 4 below.

The program shall accept any number of resistors, nodes, and resistors per node using linked lists

The program will no longer require or accept the maxVal command, and also need not accept the printR all command

The program will now accept the delete resistor command

In the printNode all command, nodes containing no resistors shall not be printed

Your program shall implement new commands to set the voltage of a node to a xed value, and to solve for the voltages at other nodes.

ECE244 Programming Fundamentals Fall 2017

4.1 Coding Requirements

1. The Standard Template Library (STL) shall not be used – the point of this assignment is for you to create your own linked list implementation

2. There shall be no prede ned maximum number of resistors, nodes, or resistors per node

3. No global variables shall be used

4. Linked lists shall be used to replace the array of resistors, nodes, and resistors attached to each node

5. All class data member variables, including Node and Resistor, shall be of private access type

6. The corresponding Resistor object(s) shall be deleted (memory freed) when the deleteR command is entered

7. The program shall not leak memory

4.2 Input

The commands your program must accept, the output each generates if it successful, and the action to take are listed in Table 1. Commands that are new to this lab are in the top portion of the table, while those that are carried over from Lab 3 are in the lower part of the table.

For each valid line of input (i.e. each line not causing an error as de ned in Section 4.3), one or more lines of output shall be produced as described in Table 1 and below. The values in italics must be replaced by either the value given in the command, or the value already stored (eg. resistance old in the modifyR output de ned in Table 1). Strings must be reproduced exactly as entered. An example session is provided in Sec 5 to illustrate this.

4.3 Error Checking

Input shall be checked for errors as described in Lab 3, except that the program shall no longer produce errors for \resistor array is full” or \node is full” because the linked list implementation has no set maximum size. There is also no longer an error for node values being out of range { any integer is now a valid node id (even a negative integer). Table 2 lists the errors for which your program must check. If more than one error occurs on a line of input, only one error message shall be issued: the rst error message occuring as arguments are processed from left to right. If a single argument has more than one error, the one listed rst in Table 2 should be printed.

4.4 Output

4.4.1 printR and printNode command output

Resistance information should be printed identically to Lab 3, except that the printR all com-mand will not be used or tested in this lab. Node information should be printed in the same way as Lab 3, except that nodes with no resistors should not be printed. Nodes shall be printed in ascending order of node ID, and the resistors attached to a node shall be printed in the order in which they were added to the node.

ECE244 Programming Fundamentals Fall 2017

Command	Arguments	Output if valid			Action if valid
setV	nodeid voltage	Set: node nodeid to voltage Volts			Updates the speci ed node voltage
					data member. This corresponds to
					connecting this node to a voltage
					source.
unsetV	nodeid	Unset: the solver will determine			Updates the speci ed node to
		the voltage of node nodeid			mark its voltage as unknown (no
					longer connected to a voltage
					source).
solve		Solve: node voltage info (see be-			Runs a numerical solution tech-
		low)			nique to determine the voltage of
					all nodes that do not have their
					voltages set.
deleteR	name	Deleted: resistor name			The speci ed resistor is removed
					from the lists.
deleteR	all	Deleted: all resistors			All resistors deleted so we have an
					empty network
insertR	name resistance	Inserted: resistor name resistance			Adds a new resistor to the resistor
	nodeid nodeid	Ohms nodeid -> nodeid			linked lists in both nodes
modifyR	name resistance	Modi ed: resistor name from re-			Updates the resistance of a resis-
		sistance		old Ohms to resistance	tor; note that this resistor must be
		Ohms			updated in the linked lists within
					two nodes.
printR	name	Print: resistor info (see below)			No data changed
printNode	nodeid	Print: node info (see below)			No data changed
printNode	all	Print: node info (see below)			No data changed

Table 1: Valid commands and arguments

ECE244	Programming Fundamentals		Fall 2017
Error message		Cause
Error: no nodes have their voltage		The solve command was run, but no nodes to which resistors
set		are attached have a set (known) voltage.	No solution can be
		found in this case.
Error: resistor name not found		When searching for a resistor by name (eg. in modifyR, printR,
		deleteR), a resistor with the given name was not found
Error: resistor name already exists		When adding a new resistor, the resistor name alread exists
Error: node nodeid not found		Whe setting/unsetting; a node with the given nodeid was not
		found

Table 2: Errors to be reported in this lab.

4.4.2 solve command

The solve command rst determines the voltage of every node, and then it prints the voltage of every node in ascending node order. To nd the voltage at every node in a network, we can follow the iterative procedure below.¹

Initialize the voltage of all nodes without a specified (setV) voltage to 0. while (some node’s voltage has changed by more than MIN ITERATION CHANGE) f

for (all nodes without a set voltage) f

set voltage of node according to Eq. 3

g

g

The voltage of a node is computed from the voltages of its neighbours according to Kircho ’s current equation, which states that the total current entering or leaving a node must be 0. Consider node₀ below, which is surrounded is connected by 3 resistors to 3 other nodes, as shown in Fig. 1. The total current entering node₀ must be 0:

Ia + Ib + Ic = 0

(1)

We can rewrite this using the fact that the current through each resistor is simply the voltage across it divided by its resistance.

V1

V0

+

V2

V0

+

V3

V0

= 0

(2)

Ra

Rb

Rc

Rearranging and solving for the voltage at node0, V0

, yields:

V0 =

1

V1

+

V2

V3

Ra

+ Rb

+ Rc

Ra

Rb

Rc

1

1

1

+

(3)

¹The iterative procedure we are using to solve for the node voltages is called the Gauss-Seidel method. It is a very general method of solving linear systems of equations, and is used to solve circuits and other systems of equations with thousands or even millions of unknowns.

ECE244 Programming Fundamentals Fall 2017

Node 2

ECE244 Programming Fundamentals Fall 2017

Node 3: -0.02 V

Node 4: -0.60 V

Node 5: 0.52 V

Node 6: 1.00 V

• Sample Session

> insertR R1 100 6			5
Inserted: resistor			R1	100.00	Ohms 6 -> 5
> insertR R2	100	5	2
Inserted: resistor			R2	100.00	Ohms 5	-> 2
> insertR R3	200	5	3
Inserted: resistor			R3	200.00	Ohms 5	-> 3
> insertR R4	150	2	3
Inserted: resistor			R4	150.00	Ohms 2	-> 3
> insertR R5	120	3	4
Inserted: resistor			R5	120.00	Ohms 3	-> 4

> solve

Error: no nodes have their voltage set

> setV 6 1

Set: node 6 to 1.00 Volts

> setV 4 -0.6

Set: node 4 to -0.60 Volts

• solve Solve:

Node 2: 0.30 V

Node 3: -0.02 V

Node 4: -0.60 V

Node 5: 0.52 V

Node 6: 1.00 V

• unsetV 4

Unset: the solver will determine the voltage of node 4

• solve Solve:

Node 2: 1.00 V

Node 3: 1.00 V

Node 4: 1.00 V

Node 5: 1.00 V

Node 6: 1.00 V

• setV 4 -0.6

Set: node 4 to -0.60 Volts

> modifyR R5 1000

Modified: resistor R5 from 120.00 Ohms to 1000.00 Ohms

• solve Solve:

Node 2: 0.81 V

Node 3: 0.72 V

Node 4: -0.60 V

Node 5: 0.87 V

Node 6: 1.00 V

• printR R5 Print:

R5 1000.00 Ohms 3 -> 4

• printNode 2 Print:

Connections at node 2: 2 resistor(s)

R2 100.00 Ohms 5 -> 2

ECE244 Programming Fundamentals Fall 2017

Figure 3: Suggested data structure. The state shown is what would exist after the commands insertR R20 100 1 3 and insertR Rfb 100 1 7.

ECE244 Programming Fundamentals Fall 2017

Likewise, functions that may be useful in ResistorList include:

Insert a resistor at the end of the list

Find a resistor by name, returning a pointer to it Delete a resistor given a pointer

• Helpful Hints

You should re-use your code from the previous lab to the extent possible. You will need to alter the data structures, and possibly make small output alterations.

The global variables that hold the node and resistor arrays in Lab 3 should be deleted. Their functionality will now be provided by objects of class NodeList and ResistorList.

To avoid use of global variables, you should create your NodeList object within main() and pass a reference to it (NodeList&) to any function that needs access (eg. your parser, add/change/remove commands, etc.)

You will need new data members in class Node to store the voltage, and whether the node has a xed voltage (setV) or not.

Each block of memory allocated by new must be freed by delete exactly once.

The linked list will start empty. You will need to create objects of class Node as you go (as they are referenced by resistors that are added). It may be useful to you to create Node* NodeList::findOrInsert(int nodeID) which nds or creates a node with the given ID.

When using dynamic memory, think carefully if a class needs a destructor and what objects it might need to delete (hint: anything where the class holds the only pointer to a memory block allocated with new).

Listing all nodes correctly will be made easier if you maintain your node list in ascending order of node ID.

If you use the suggested data structure, remember when adding/changing resistors that you will have two copies of each resistor.

Use of the valgrind memory tester is strongly recommended to catch invalid reads, writes, and allocation/deallocation. It will tell you when and on what function and line the error occurs. For memory leaks, it will tell you where the leaking block was allocated.

There are several corner cases that, in principle, require special handling. However, you should ignore these cases and your code will NOT be tested against these cases.

{ It is possible to have nodes that are not connected to anything. You should ignore this case.

{ It is also possible to have two disjoint networks, one with voltage and one that is \ oat-ing”. You should also ignore this case.

{ You may assume that no resistor will have a 0 value.

{

ECE244 Programming Fundamentals Fall 2017

• Procedure

Create a lab4 folder with appropriate permissions in your ece244 directory. Before submitting, remember to use exercise, plus to make some test cases of your own as exercise will not test all cases.

• Deliverables

You must submit all source les to permit your project to compile. They should be:

Main.cpp

Rparser.cpp and Rparser.h

ResistorList.h and ResistorList.cpp Resistor.h and Resistor.cpp

Node.h and Node.cpp

NodeList.h and NodeList.cpp

Submit the les using

~ece244i/public/submit 4

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