Plot Piecewise function graph

Here's my code but i can't get the graph as shown in the picture.

% Use conditional statements and loops to calculate function values for
% different input ranges
x = -2.99*pi: 0.01: 3*pi;       % Create domain from -2.99pi to 3pi, at increment of 0.01
y = zeros(1,length(x));
for i = 1: length(x)        % For each statement i, it will pass through each value of x
    if x(i) > -3*pi && x(i) < -pi       % If x lies at −3pi < x <-pi, 
        y(i) = 1./log(2)*sin(x(i));        % the function is y = 1/(ln2)(sinx)
    elseif x(i) >= -pi && x(i) <=2      % If x lies at -pi <= x <= 2, 
        y(i) = abs(x(i)) - 3;               % the function is y = |x| -3
    else 
        y(i) = exp(1);      % If x doesn't lies at above interval, the function is y = e
    end
end
plot(x, y); 
text(3.2\pi, 0.2 , 'x'); text(0.2\pi, 3.5, 'y');  
axis([-4\pi 4\pi -4 4]);
xticklabels({'-3\pi', '-2\pi', '-\pi', '0', '\pi', '2\pi', '3\pi'});    % Display tick marks along the x-axis by specifying the text to show pi symbol
yticks(-3: 1: 3);    % Display tick marks along the y-axis 0.5,1 and 1.5
box off;

**This is the graph should be look like.

[L]

How to create asymptotes?

Answer 1

[Paul]

This line

  y(i) = 1./log(2)*sin(x(i));

is incorrect.

The order of operations for multiplication and division is that they are evaluated in order from left to right. So that line could also be expressed as

  y(i) = ( 1./log(2) ) * sin(x(i));

i.e., the division is done first, and the result of the division becomes the first operand for the multiplication.

Hopefully that gives you a clue as to how to fix the code (at least that part of it).

[Alexander]

I can't see a difference in the outcome between both equations.

[Paul]

Can't see a difference in the outcome betwee which equations? Can you show the equations being referenced?

[Alexander]

The line

y(i) = 1./log(2)*sin(x(i));

and the line

y(i) = ( 1./log(2) ) * sin(x(i));

have the same result. If I misunderstood, please give some advice.

[Paul]

Yes, those two lines do yield the same result. The first line is used in the code in the question. I used the extra parentheses in the second to emphasize the order of operations used to evaluate the first.

Neither of those lines are a correct implementation of

which was the point I was trying to make to lead the OP to the correct Matlab expression. I think the OP did eventually get the correct expression, but that comment has since been deleted.

[Alexander]

Thanks.

Answer 2

[Star Strider]

To do this in the Symbolic Math Toolbox, just write it essentially as in your original post —

syms x 
f(x) = piecewise((-3*pi<x<-pi), 1/(log(2)*sin(x)), (-pi<=x<=2), abs(x)-3, (2<x<=3*pi), exp(1))

f(x) = 

figure
fplot(f, [-4*pi  4*pi], 'MeshDensity',1E2)
grid
ylim([-1 1]*5)

.

[L]

how to remove the asymptote for x=-2pi?

[Star Strider]

First, turn all of them off, then re-draw the ones you want using the xline funciton —

syms x 
f(x) = piecewise((-3*pi<x<-pi), 1/(log(2)*sin(x)), (-pi<=x<=2), abs(x)-3, (2<x<=3*pi), exp(1))

f(x) = 

figure
hfp = fplot(f, [-4*pi  4*pi], 'MeshDensity',1E2);
grid
hfp.ShowPoles = 'off';                                  % Turn Off All Asymptotes
xline(-3*pi, '--k')                                     % Draw Asymptote At -3*pi
ylim([-1 1]*5)

.

Answer 3

[Alexander]

You should change

axis([-4\pi 4\pi -4 4]);

to

axis([-4*pi 4*pi -4 4]);

in the first step. Than you can see your complete function.