Help about function with if statement

8 次查看（过去 30 天）
Janez Novak
Janez Novak 2015-11-18
编辑： Jan 2016-12-18
I have problem with creating function. I don´t know how to use command function properly. Can you guys tell me where I was wrong it will be very helpful
function [y]=task1(x)
if x>=8
y = 14*(5*x)^(1/2)+9;
end
if (-1<=x<8)
y=9*x +9;
end
if (x<-1) y=9;
end
  1 个评论
Jan
Jan 2016-12-18
Why do you assume, that something is wrong? Which problem do you observe? Do you get an error message?

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回答（2 个）

laaj
laaj 2016-12-18
function output=task1(x)
if x>=8
y = 14*(5*x)^(1/2)+9;
end
if (-1<=x<8)
y=9*x +9;
end
if (x<-1)
y=9;
end
output=[y];
I don't know much but I just hope it will solve the problem.
Jan
Jan 2016-12-18
编辑：Jan 2016-12-18
"if (-1<=x<8)" does most likely not do, what you expect. Matlab processes this expression from left to right: "-1<=x" replies TRUE or FALSE depending on the value of x. In the next step you have "TRUE<8" or "FALSE<8". While TRUE is converted to 1, FALSE is a 0, and both values are smaller than 8. You need two comparisons: "-1 <= x" and "x < 8":
function y = task1(x)
if x >= 8
y = 14 * (5 * x)^(1 / 2) + 9;
elseif -1 <= x && x < 8
y = 9 * x + 9;
elseif x < -1
y = 9;
end
Now you can simplify this: If you have excluded x>=8 already, you do not have to check for x<8 anymore:
function y = task1(x)
if x >= 8
y = 14 * sqrt(5 * x) + 9; % SQRT is cheaper than ^0.5
elseif -1 <= x
y = 9 * x + 9;
else
y = 9;
end

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