ENGR 1181 | MATLAB 15: Functions
MAT_15D_Assignment
Follow the format that you’ve been doing for previous problems.
 Do the entire problem in one script file.
 Your script file should include comment statements to help organize your script file.
 Make sure the Command Window displays your name, the assignment name, and your group
number.
 Submit based on your instructor’s guidelines.
Background
While electrical engineers use circuits often, other types of engineers use them to perform experiments
and design products, as well. Thus, learning about basic principles of circuits is important for all
engineers.
Define
You are an electrical engineer working with some circuit boards. You have many versions of the circuit
shown below and you need to write a program to compute the equivalent resistance, 𝑅𝑒𝑞 , of the circuit
to determine which board you need to use.
Rp1
Rp2
Rs1
Rs2
RsM
Rp3
RpN
You will write a program that includes two user written functions. The first user written function will
compute the equivalent resistance from N resistors in parallel. The resistors in parallel are the ones that
are vertically stacked on top of each other. The equation for equivalent resistance, 𝑅𝑃𝑒𝑞 , of N resistors
in parallel is given below:
1
𝑅𝑃𝑒𝑞
=
1
1
1
1
+
+
+ ⋯+
𝑅𝑃1 𝑅𝑃2 𝑅𝑃3
𝑅𝑃𝑁
After computing the equivalent resistance of the parallel resistors, 𝑅𝑃𝑒𝑞 , the circuit can be redrawn,
substituting 𝑅𝑃𝑒𝑞 for the set of parallel resistors.
Rs1
Rs2
RPeq
RsM
As a result you now have a set of only resistors in series (horizontally attached to one another). The
second user written function will compute the equivalent resistance from M resistors in series. Be sure
to include the parallel equivalent resistance, 𝑅𝑃𝑒𝑞 , in this computation. The equation for equivalent
resistance, 𝑅𝑒𝑞 , of M resistors in series is given below:
𝑅𝑒𝑞 = 𝑅1 + 𝑅2 + 𝑅3 + ⋯ + 𝑅𝑀
A help sheet that includes a sample calculation is included at the end of this assignment.
The user will input the number of resistors in parallel and the number of additional resistors in series.
For example Circuit A has 4 resistors in parallel and 3 additional resistors in series. Then, the user will
input the resistance in Ohms (Ω) of each resistor, in order. Set up the program to run repeatedly until
the user quits the program.
Instructions
Represent
 Consider making a flowchart or algorithm to represent your solution process.
Plan
 Create a script file
 Include comment statements in your program to plan out the solution.
Implement
 Part 1:
 Write a function file for calculating the equivalent resistance for N resistors in parallel.
 The function should be sent a vector that contains all the resistances. You may send
other information as needed.
 The function should return the equivalent resistance.
 Print the function file to pdf and submit to the Carmen Dropbox. Continue on to Part 2.
 Part 2:
 Write a function file for the series resistors.
 In the script file, perform the following tasks:
 Prompt the user for all inputs
 Compute the equivalent resistance of the resistors using the two functions
described above.
 Display this value to the screen
 Prompt the user to see if he/she wants to quit.
 Repeat the program if necessary. You may need to clear the vectors. To clear
individual variables type clear and then the variable name.
 Use the program to determine which circuits (A-D) on the following page give an equivalent
resistance of 1300 Ω. Add an fprintf() statement to the end of your program which prints to
the command window the answer.
 Your program must be run to show the results for all 4 circuits given.
Evaluate
 Perform a hand calculation to verify your answer.
Document
 Print (paper or pdf depending on instructor preference) the final version of your script file.
 Print (paper or pdf depending on instructor preference) the command window output.
 Print (paper or pdf depending on instructor preference) the calculation for the evaluate step.
 If paper: Staple the script file, function files, output, and verification together and turn it in.
 If pdf: Combine pdf files together and submit to Carmen Dropbox.
750Ω
500Ω
1000Ω
100Ω
80Ω
1000Ω
A)
250Ω
100Ω
100Ω
500Ω
B)
500Ω
100Ω
700Ω
C)
200Ω
1000Ω
135Ω
65Ω
1000Ω
750Ω
D)
500Ω
500Ω
500Ω
Equivalent Resistance Sample Calculation
If given the circuit shown below, the following steps outline how to compute the equivalent
resistance:
5Ω
10Ω
25Ω
45Ω
65Ω
20Ω
20Ω
1) There are 4 resistors in parallel and 3 additional resistors in series.
2) Compute the equivalent resistance of the resistors in parallel (5Ω, 10 Ω, 20 Ω, 20 Ω).
1
𝑅𝑃𝑒𝑞
1
𝑅𝑃𝑒𝑞
=
=
1
1
1
1
+
+
+ ⋯+
𝑅𝑃1 𝑅𝑃2 𝑅𝑃3
𝑅𝑃𝑁
1
1
1
1
+
+
+
= 0.4
5Ω 10Ω 20Ω 20Ω
𝑅𝑃𝑒𝑞 = 2.5Ω
3) Redraw the circuit
25Ω
45Ω
65Ω
2.5Ω
4) Compute the equivalent resistance of the resistors in series (including the parallel
equivalent resistance just computed).
𝑅𝑒𝑞 = 𝑅1 + 𝑅2 + 𝑅3 + ⋯ + 𝑅𝑀
𝑅𝑒𝑞 = 25Ω + 2.5Ω + 45Ω + 65Ω
𝑅𝑒𝑞 = 137.5Ω
5) The equivalent resistance of the circuit is 137.5Ω.