# how can I write a function y(n) in terms of function x(n)?

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geometry geometry on 17 Mar 2018
Edited: Walter Roberson on 17 Mar 2018
I run this code and I get error. (the error is for function y which contains function x in its defenition). how can i fix this error? (The functions x and y are discrete signals)
syms n y x
n=-10:1:10;
x=dirac(n+1)+dirac(-n+4)-2*heaviside(n+3);
y(n)=x(n)-x(2*n+3);
plot(x,'o');
plot(y,'o');

Walter Roberson on 17 Mar 2018
syms n y x
x(n) = dirac(n+1)+dirac(-n+4)-2*heaviside(n+3);
y(n) = x(n)-x(2*n+3);
N=-10:1:10;
plot(N, subs(x,n,N), 'ko', N, subs(y,n,N), 'bo')
It will not look like much, since dirac() is only ever 0 or infinity.
Walter Roberson on 17 Mar 2018
"which function should I use for discrete dirac signals? (i.e the function that is only one in time zero)"
You can use
Dirac = @(x) not(x)
if you can be certain that none of the values are nan. If nan is a possibility then use
Dirac = @(x) x == 0;
However, if you are working with symbolic values, then you need
Dirac = @(x) piecewise(x == 0, 1, 0)

elham kreem on 17 Mar 2018
if you run x , it is a vector 1x21 , then when you used for y(n) , you will get for x a subscript more
than 21 ,such as if you have n=10 then you have x(23) , and this is not found.the result, it is not run