Description

Introduction to Programming with MATLAB
Lesson 5

• Unless otherwise indicated, your function should not print anything to the Command Window, but your function will not be counted incorrect if it does.
• Note that you are not required to use the suggested names of input variables and output variables, but you must use the specified function names.
• Finally, read the instructions on the web page on how to test your functions with the auto-grader program provided, and what to submit to Coursera to get credit.
• Note that starred problems, marked by ***, are harder than usual, so do not get discouraged if you have difficulty solving them.

1. Write a function called generationXYZ that takes as its only input argument one positive integer specifying the year of birth of a person and returns as its only output argument the name of the generation that the person is part of (‘X’, ‘Y’, or ‘Z ‘) according to the table below. For births before 1966, return ‘O’ for Old and for births after 2012, return ‘K’ for Kid. Remember that to assign a letter to a variable, you need to put it in single quotes, as in: gen = ‘X’.

Generation Born
X 1966-1980
Y 1981-1999
Z 2000-2012
2. Write a function called letter_grade that takes a positive integer called score as its input argument and returns a letter grade according to the following scale: A: 91 and above; B: 81-90; C: 71-80; D: 61-70; F: below 61. Remember that to assign a letter to a variable, you need to put it in single quotes, as in: grade = ‘A’.
4. Write a function called classify that takes one input argument x. That argument will have no more than two dimensions. If x is an empty matrix, the function returns -1. If x is a scalar, it returns 0. If x is a vector, it returns 1. Finally, if x is none of these, it returns 2. Do not use the built-in functions isempty, isscalar, or isvector.

7. Consider the definition: function [s1, s2, sums] = sines(pts,amp,n1,n2). The input, pts, is an integer, but amp, n1, and n2 and are not necessarily integers. Output argument s1 is a row vector whose length (number of elements) equals pts. The elements of s1 are the values of the sine function when it is given equally spaced arguments that start at zero and extend through n1 periods of the sine. (Note that we ask for full periods, so if n1 is an integer, both the first and the last element of s1 will be 0 other than a very small rounding error.) (Hint: if you have to make a 100m straight fence from 10m long segments, how many segments do you need? And how many poles?) The amplitude of the sine wave equals amp. The vector s2 is the same as s1 except that s2 contains n2 periods. The vector sums is the sum of s1 and s2. If n2 is omitted, then it should be set to a value that is 5% greater than n1. If n1 is omitted also, then it should be set to 100. If amp is not provided, then it should default to 1. Finally, if pts is omitted as well, then it should be set to 1000. If you run sines as shown below and plot the third output argument, sums, the figures should look like these (if you stretch the plot windows horizontally):

[s1, s2, sums] = sines(10,1,2,3); [s1,s2,sums] = sines(1000,1,50,52);
8. *** Write a function called moving_average that takes a scalar called x as an input argument and returns a scalar. The value it returns depends not only on the input but also on previous inputs to this same function when the function is called repeatedly. That returned value is a “moving average” of those inputs. The function uses a “buffer” to hold previous inputs, and the buffer can hold a maximum of 25 inputs. Specifically, the function must save the most recent 25 inputs in a vector (the buffer) that is a persistent variable inside the function. Each time the function is called, it copies the input argument into an element of the buffer. If there are already 25 inputs stored in the buffer, it discards the oldest element and saves the current one in the buffer. After it has stored the input in the buffer, it returns the mean of all the elements in the buffer. Thus, for each of the first 24 calls to the function, the function uses only the inputs it has received so far to determine the average (e.g., the first call simply returns x, the second call averages x and the input from the first call, etc.), and after that, it returns the average of the most recent 25 inputs.
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