If Statement not working

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isabella Anglin
isabella Anglin 2020-10-16
评论： Ameer Hamza 2020-10-16
Hello,
I am new to matlab and have a very, very basic issue. This is a simplified function, but it illustrates the problem I have in my other function.
Matlab seems to bypass my if conditions. Here is the function:
function y = functry(x)
Speed = 100;
if (x> 100)
Speed = 50;
end
y = Speed * x;
end
However, the Speed is taken to be 100 even when I input a high range, for example:
y_try = functry(1:150)
plot(1:150, y_try)
Here is still get a linear plot and no change for the Speed when x>100.
Any help would be much appreciated! Thank you!

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Ameer Hamza
Ameer Hamza 2020-10-16
编辑：Ameer Hamza 2020-10-16
If x is a vector then the line
if (x> 100)
does not work as expected. The correct syntax is
function y = functry(x)
Speed1 = 100;
Speed2 = 50;
mask = x > 100;
y = (~mask)*Speed1.*x + mask*Speed2.*x;
end
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isabella Anglin
isabella Anglin 2020-10-16
Okay great thank you!
However, eventually in my function i'll want to have multiple "Speeds". Do i just make additional masks then?
Ameer Hamza
Ameer Hamza 2020-10-16
Yes. Let me show you a more general approach
function y = functry(x)
Speed1 = 100;
Speed2 = 50;
mask1 = x < 100;
mask2 = x >= 100;
y = (mask1)*Speed1.*x + mask2*Speed2.*x;
end
Just keep making a mask like this, and it will work. Note that If you want to have a condition that x is between 150 to 250, then the correct syntax to write that is
mask = (150 < x) & (x < 250) % mask = 150 < x < 250 is a common mistake.

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