diff --git a/dependencies/reactor_class.js b/dependencies/reactor_class.js
index 2c8d3b8..6dd6168 100644
--- a/dependencies/reactor_class.js
+++ b/dependencies/reactor_class.js
@@ -2,7 +2,7 @@ const ASM3 = require('./asm3_class')
 const { create, all } = require('mathjs')
 
 const config = {
-  matrix: 'Array' // Choose 'Matrix' (default) or 'Array'
+  matrix: 'Array' // choose 'Matrix' (default) or 'Array'
 }
 
 const math = create(all, config)
@@ -185,7 +185,8 @@ class Reactor_PFR {
             const BC_gradient = Array(this.n_x).fill(0.0);
             BC_gradient[0] = -1;
             BC_gradient[1] = 1;
-            const BC_dispersion = math.multiply(this.alpha*this.D * this.A / (math.sum(this.Fs)*this.d_x), [BC_gradient], new_state)[0];
+            let Pe = this.length*math.sum(this.Fs)/(this.D*this.A)
+            const BC_dispersion = math.multiply((1-(1+4*this.volume/math.sum(this.Fs)/Pe)^0.5)/Pe, this.D * this.A / (math.sum(this.Fs)*this.d_x), [BC_gradient], new_state)[0];
             console.log(math.add(BC_C_in, BC_dispersion));
             new_state[0] = math.add(BC_C_in, BC_dispersion).map(val => val < 0 ? 0 : val);