Why are complex values obtained for the below function (x) in the if condition?

Hi there! I'm facing an issue with the below function. The function is supposed to generate values for x that are not imaginary. However, I'm getting a warning: "Imaginary parts of complex X and/or Y arguments ignored." To be more specific, unlike the output shown in the figure, when y is equal to 0, the function should calculate x=0. Can you please assist me in finding out what could be causing this issue?

clc
close all
clear all

a = 280;
b = 580;
c = 0.35;
d =1.71E5;
e = 7;
f = 1+(3.5*(a/b));
g = d/(1+(0.002*e*(d/a)));

y = (0:2.5:b);

if any(y <= a)
   x = (y/d)+(0.002*((y/a).^e));
   if any(y > a)
   x = 0.002+(a/d)+((y-a)/g)+(c.*(((y-a)/(b-a)).^f));
   end
end

plot(x,y)

Warning: Imaginary parts of complex X and/or Y arguments ignored.

xlabel('x')
ylabel('y')

Answer 1

[Matt J]

Because you are raising a negative number to a fractional power, e.g.,

(-2)^1.5

ans = 0.0000 - 2.8284i

[Matt J]

Perhaps,

a = 280;
b = 580;
c = 0.35;
d =1.71E5;
e = 7;
f = 1+(3.5*(a/b));
g = d/(1+(0.002*e*(d/a)));
y = (0:2.5:b);

 x = (y/d)+(0.002*((y/a).^e));

 r=(y>a); 
 x(r)= 0.002+(a/d)+((y(r)-a)/g)+(c.*(((y(r)-a)/(b-a)).^f));
 
plot(x,y)
xlabel('x')
ylabel('y')

Answer 2

[Torsten]

Maybe you mean

clc
close all
clear all
a = 280;
b = 580;
c = 0.35;
d =1.71E5;
e = 7;
f = 1+(3.5*(a/b));
g = d/(1+(0.002*e*(d/a)));
y = (0:2.5:b);

x = zeros(size(y));
idx = y<=a;
x(idx) = (y(idx)/d)+(0.002*((y(idx)/a).^e));
x(~idx) = 0.002+(a/d)+((y(~idx)-a)/g)+(c.*(((y(~idx)-a)/(b-a)).^f));
plot(x,y)
xlabel('x')
ylabel('y')