Plot x and y with two function

Question

Dani D 2016-4-25

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编辑： Star Strider 2016-4-25

Hello, I want plot x and y , but i can't

x = rand(65000,1);
        if  x <= 0.5
             y =  sqrt(x);
          elseif x > 0.5
              y = x^1.25;
          end
   plot(x,y);

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Answer 1

Star Strider 2016-4-25

0
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I am not certain what you are doing with ‘x’ being random, but this will work:

x = rand(65000,1);
y = (x <= 0.5).*(sqrt(x)) + (x > 0.5).*(x.^1.25);
figure(1)
plot(x, y)
grid

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Dani D 2016-4-25

No , I have if else. If less or equal 0.5 we have sqrt(x) else if greater than 0.5 we have x^1.25

Star Strider 2016-4-25

编辑：Star Strider 2016-4-25

在 MATLAB Online 中打开

That is what my code does. It uses logical index ‘masking’ instead of an if block.

The logical mask is equal to 1 where the logical condition is true (and is multiplied by the value of the function at that value of ‘x’) and 0 where the logical condition is false, so the value for that particular condition would be 0. The code for ‘y’ adds the two conditions together with respect to their function values over each condition to create a continuous vector.

EDIT — This is a much less efficient way of doing it, but it produces the same result:

x = rand(65000,1);
for k1 = 1:length(x)
    if  x(k1) <= 0.5
        y(k1) =  sqrt(x(k1));
    elseif x(k1) > 0.5
        y(k1) = x(k1)^1.25;
    end
end
plot(x,y);