diff --git a/examples/plot_ista.py b/examples/plot_ista.py
index d6359905..c8c3d71a 100755
--- a/examples/plot_ista.py
+++ b/examples/plot_ista.py
@@ -12,7 +12,9 @@
 mathematically translates to solving the following constrained problem:
 
 .. math::
-    \quad \|\mathbf{Op}\mathbf{x}-  \mathbf{b}\|_2 <= \sigma,
+    \|\mathbf{x}\|_0 \quad  \text{subject to} \quad
+    \|\mathbf{Op}\,\mathbf{x}-\mathbf{y}\|_2^2 \leq \sigma^2,
+
 
 while IRLS, ISTA and FISTA solve an uncostrained problem with a L1
 regularization term: