math - 八度：在列表中的范围内测试函数或使用 For 循环？

Question

我想查看具有不同 x 值的函数 y(x) 的值，其中 y(x) < 5：

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

我该怎么做？

Answer 1

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 2

您可以只创建一个值向量x，然后查看向量y，或绘制它：

% 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 3

如果您限制x范围[-6 4]，它将确保y限制在小于或等于 5。在 MATLAB 中，您可以使用FPLOT（如Amro 建议）或LINSPACE和PLOT（如Peter 建议）绘制函数：

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 

Answer 4

% 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))