Using a fucntion in loop

I defined this;

P = [1 -2 4]

I want to find nth derivative of this poly and I want to do it with while loop for example I try this;

a = 0;
n = 3;
while(a < n)
polyder(P)
a=a+1;
end

The result is

ans =
     2    -2
ans =
     2    -2
ans =
     2    -2

Why does the program take derivative of the poly at first but it does not for the rest of it?

Answer 1

[Torsten]

P = [1 -2 4]

P = 1×3

1 -2 4

a = 0;
n = 3;
while(a < n)
    P = polyder(P)
    a = a + 1;
end

P = 1×2

2 -2

P = 2

P = 0