Octave: testing functions over a Range in Lists or like with For-loops?

Question

I want to see the values of the function y(x) with different values of x, where y(x) < 5:

y = abs(x)+abs(x+2)-5

How can I do it?

Answer 1

You can just create a vector of values x, then look at the vector y, or plot it:

% Create a vector with 20 equally spaced entries in the range [-1,1].
x = linspace(-1,1,20);

% Calculate y, and see the result
y = abs(x) + abs(x + 2) - 5

% Plot.
plot(x, y);

% View the minimum and maximum.
min(y)
max(y)

Answer 2

% create a vector x with values between 1 and 5
x = 1:0.1:5;

% create a vector y with your function
y = abs(x) + abs(x+2) - 5;

% find all elements in y that are under 5
y(find(y<5))

Answer 3

fplot(@(x) abs(x)+abs(x+2)-5, [-10 10])
hold all
fplot(@(x) 5, [-10 10])
legend({'y=abs(x)+abs(x+2)-5' 'y=5'})

Answer 4

If you limit x to the range [-6 4], it will ensure that y will be limited to less than or equal to 5. In MATLAB, you can then plot the function using FPLOT (like Amro suggested) or LINSPACE and PLOT (like Peter suggested):

y = @(x) abs(x)+abs(x+2)-5;  % Create a function handle for y
fplot(y,[-6 4]);             % FPLOT chooses the points at which to evaluate y
% OR
x = linspace(-6,4,100);      % Create 100 equally-spaced points from -6 to 4
plot(x,y(x));                % PLOT will plot the points you give it