"fix math"

python/paddle/fluid/layers/nn.py

@@ -4210,9 +4210,7 @@ def lrn(input, n=5, k=1.0, alpha=1e-4, beta=0.75, name=None):
 
     .. math::
 
-      Output(i, x, y) = Input(i, x, y) / \left( \\
-        k + \alpha \sum\limits^{\min(C, c + n/2)}_{j = \max(0, c - n/2)} \\
-        (Input(j, x, y))^2\right)^{\beta}
+      Output(i, x, y) = Input(i, x, y) / \\left(k + \\alpha \\sum\\limits^{\\min(C, c + n/2)}_{j = \\max(0, c - n/2)}(Input(j, x, y))^2\\right)^{\\beta}
 
     In the above equation: