Complex Numbers where thy are not supposed to be

Hi I had this Problem a number of times now and I dont get it.

I get Complex Numbers as results, however i need normal Numbers.

I simplified the code. its a sinus going through an dsp algorithm for an audio plugin.

The negative Halfwave of the Sinus causes the output to become Complex.

1-1^2.5 = 0

but when i run the code i get

1-1^2.5= 1.0000 + 1.0000i

How can i tell matlab that no Complex Calculus is needed ?

x=[0 ; 1 ; -1 ; 0]
N = length(x);
y=zeros(N,1)

for n=1:N
     y(n,1) = (1+x(n,1)^2.5)
end
 
%thank u in advance ;)

Answer 1

[Jan]

1 - 1^2.5 == 0    % Let's ignore the rounding errors...

This is correct. But you calculate something else:

x = -1;
1 + x^2.5

This is:

1 + (-1)^2.5

which is 1 + 1i. The parentheses matter. Or if you store the -1 in a variable, the code is equivalent to:

1 + (x)^2.5

"How can i tell matlab that no Complex Calculus is needed?"

You can't. The result of 1+(x)^2.5 with a negative x is complex and you cannot convert this to 0 - except with catching these values explicitly:

y = zeros(N, 1);
for n = 1:N
    if x(n) >= 0
       y(n) = 1 + x(n)^2.5;
    end
end

[Steven Lord]

Another possibility is that the poster intended to raise the expression to the 2.5 power not just the variable.

x = -1;
y1 = (1+x^2.5)

y1 = 1.0000 + 1.0000i

y2 = (1+x)^2.5

y2 = 0

Of course in this case there's no need for a loop with the example as written if you use the elementwise power operator .^ instead of the matrix power operator ^ as below.

x = [0 1; -1 0];
y3 = (1+x).^2.5

y3 = 2×2

1.0000 5.6569 0 1.0000

[Adrian Alexander]

thank u i got it and made it work ^^