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

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');

Answer 1

[Walter Roberson]

 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.

[geometry geometry]

Thanks... could you explain the line 5 ?

I think it only plots the function x?

[geometry geometry]

Another question is that I think I can't use dirac(n) for discrete-time signals.

which function should I use for discrete dirac signals? (i.e the function that is only one in time zero)

[Walter Roberson]

Calls of the form

plot(x1, y1, x2, y2)

are the same as

ax = gca;
curhold = get(ax, 'NextPlot');
plot(ax, x1, y1);
set(gca, 'NextPlot', 'add')
plot(x2, y2);
set(ax, 'NextPlot', curhold)

That is, passing multiple x, y pairs into plot() causes both lines to be plotted.

So the N, subs(x,n,N) part causes x to be plotted, and the N, subs(y,n,N) causes y to be plotted.

This might have given you the impression that y was not plotted because the y values consist only of 0s and infinities.

[Walter Roberson]

"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)

Answer 2

[elham kreem]

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