Why can't I get the left arrow to work?

Question

$$
\xymatrix{\ar @{} [dr]
x[n] \ar[d] \ar[r]^-{DTFT} & X(e^{j\omega}) \ar[r]^-{Sample} & X(k) \ar[d] \\
  \ar[r]^-{\neq} & {x_1[n]} & {IDFT_N\{ X(k)\}} \ar{l}} 
$$

Produces this result:

I simply want the arrow to point to the result and I have tried a few different things but it is simply not working. I got all of the from the manual btw... Any help would be appreciated!

Answer 1

I have fixed the code a bit and the end result should be what you wanted.

\documentclass[a4paper,12pt]{article}
\usepackage[all]{xy}
\begin{document}
[\xymatrix{\ar @{} [dr]
x[n] \ar[d] \ar[r]^-{\mathrm{DTFT}} & X(e^{j\omega}) \ar[r]^-{\mathrm{Sample}} & X(k) \ar[d] \
  \ar[r]^-{\neq} & {x_1[n]} \ar[r] & {\mathrm{IDFT}_N{ X(k)}}
  } ]
\end{document}

Drawing with the left arrow.

\documentclass[a4paper,12pt]{article}
\usepackage[all]{xy}
\begin{document}
[\xymatrix{\ar @{} [dr]
x[n] \ar[d] \ar[r]^-{\mathrm{DTFT}} & X(e^{j\omega}) \ar[r]^-{\mathrm{Sample}} & X(k) \ar[d] \
  \ar[r]^-{\neq} & {x_1[n]}  &\ar[l] {\mathrm{IDFT}_N{ X(k)}}
  } ]
\end{document}