Question

Problem 1 (20 pts)
Global variables are declared outside any function and can be accessed by any function in MATLAB. In contrast, local variables are declared inside a function, and can be used only inside that function. In this homework, you will create two global variables containing x and y coordinates of points to be plotted. You will also create a plotting function which will access the global variables.
a) Create the function plotFunct with no inputs and no outputs. Declare two global variables named x and y inside the function. This function will create a new figure and plot y vs x using green dots. Label the x-axis ’x data’ and y-axis ’y data’.
b) In a new script, declare two global variables x and y.
c) Initialize x to an array from 0 to 10 with a step size of 0.25.
d) Initialize y to be a function of x squared, then call the plotFunct to plot the global variables.
e) Repeat part d with y as the square root of x.
f) Repeat part d again with y as the natural log of x.
Note: Your code should produce three separate figures, one for each call made to plotFunct.
Please submit both .m files.

Answer 1

Note:

1. Two files have been created namely plotfunc.m and test.m

2. plotfunc.m has a function which is used to plot the graph and test.m is the script which contains the values of global variables x and y.

3. Run the test.m script to see the output plots.

4. Please set the octave or matlab working directly properly.

Code in plotfunc.m

function plotfunc()
   % x and y are global variables.
   global x;
   global y;
  
   %Using plot function to plot graph in dotted green.
   plot(x, y,'g:');
  
   %Labelling x and y axes.
   ylabel('y data');
   xlabel('x data');
end

Codes in test.m

1. For square function: (y = x²)

% x and y are global variables.
global x = []
global y = []

r = 1;

% Initializing each element of x.
for i=0:0.25:10
x(r) = i;
r = r+1;
end

% Initializing y as a square of x.
for i=1:length(x)
y(i) = x(i)^2;
end

plotfunc();

2. For square root function: y = sqrt(x) or y = x^0.5

% x and y are global variables.
global x = []
global y = []

r = 1;

% Initializing each element of x.
for i=0:0.25:10
x(r) = i;
r = r+1;
end

% Initializing y as a square root of x.
for i=1:length(x)
y(i) = x(i)^0.5;
end

plotfunc();

3. For natural log function: (y = ln x)

% x and y are global variables.
global x = []
global y = []

r = 1;

% Initializing each element of x.
for i=0:0.25:10
x(r) = i;
r = r+1;
end

% Initializing y as a square root of x.
for i=1:length(x)
%In matlab natural log is donated by log function.
y(i) = log(x(i));
end

plotfunc();

Output plots:

1.

2.

3.