From 2174113e7df8fd25f4af51c6ad6c54143b5d2d80 Mon Sep 17 00:00:00 2001
From: Colin <colin@uninsane.org>
Date: Sun, 12 Jul 2020 21:35:40 -0700
Subject: [PATCH] Fix the inverted sign so that the energy looks reasonable now

---
 examples/coremem.rs |  3 ++-
 src/lib.rs          | 21 +++++++++++----------
 src/render.rs       |  8 ++++----
 3 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/examples/coremem.rs b/examples/coremem.rs
index b36e1af..686aa3f 100644
--- a/examples/coremem.rs
+++ b/examples/coremem.rs
@@ -4,7 +4,8 @@ use std::{thread, time};
 
 fn main() {
     let mut state = SimState::new(16);
-    state.impulse_e(10, 1.0);
+    state.impulse_e(0, 1.0);
+    state.impulse_e(15, 1.0);
     loop {
         NumericTermRenderer.render(&state);
         state.step();
diff --git a/src/lib.rs b/src/lib.rs
index 5271aaf..437a5b6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -17,7 +17,8 @@ pub mod render;
 mod consts {
     /// Speed of light in a vacuum; m/s.
     /// Also equal to 1/sqrt(epsilon_0 mu_0)
-    pub const C:f32 = 299792458f32;
+    pub const C: f32 = 299792458f32;
+    // pub const Z0: f32 = 376.73031366857f32;
 }
 
 #[derive(Default)]
@@ -103,16 +104,16 @@ impl Cell {
 
     fn step_e(self, left: Cell) -> Self {
         // Maxwell's equation: del x B = mu_0 eps_0 dE/dt
-        // Expands: -dB_z/dx = mu_0 eps_0 dE_y/dt
-        // Rearrange: dE_y/dt = -1/(mu_0 eps_0) dB_z/dx
-        // Discretize: (delta E_y)/(delta t) = -1/(mu_0 eps_0) (delta dB_z)/(delta x)
-        // Rearrange: delta E_y = (delta t)/(delta x) 1/(mu_0 eps_0) (-delta B_z)
-        // Substitute c as in step_b: delta E_y = (mu_0 eps_0)/c (-delta B_z)
+        // Expands: dB_y/dx = mu_0 eps_0 dE_y/dt
+        // Rearrange: dE_y/dt = 1/(mu_0 eps_0) dB_y/dx
+        // Discretize: (delta E_y)/(delta t) = 1/(mu_0 eps_0) (delta dB_y)/(delta x)
+        // Rearrange: delta E_y = (delta t)/(delta x) 1/(mu_0 eps_0) (delta B_y)
+        // Substitute c as in step_b: delta E_y = (mu_0 eps_0)/c (delta B_y)
         // Note that c = 1/sqrt(mu_0 eps_0), so this becomes:
-        // delta E_y = c (-delta B_z)
-        // XXX once again this diffes from [1]
-        let delta_b = self.by - left.by;
-        let delta_e = (-delta_b) * consts::C;
+        // delta E_y = c (delta B_y)
+        // XXX once again this differs from [1]
+        let delta_b = self.by - left.by; //< delta B_y
+        let delta_e = delta_b * consts::C; //< delta E_z
         Cell {
             ez: self.ez + delta_e,
             by: self.by,
diff --git a/src/render.rs b/src/render.rs
index f921559..00e61db 100644
--- a/src/render.rs
+++ b/src/render.rs
@@ -4,13 +4,13 @@ pub struct NumericTermRenderer;
 
 impl NumericTermRenderer {
     pub fn render(&self, state: &SimState) {
-        print!("E:   ");
+        print!("E:");
         for cell in state.cells() {
-            print!("{:>8.1e} ", cell.ez());
+            print!("{:>10.1e} ", cell.ez());
         }
-        print!("\nB:   ");
+        print!("\nB:      ");
         for cell in state.cells() {
-            print!("{:>8.1e} ", cell.by());
+            print!("{:>10.1e} ", cell.by());
         }
         print!("\n");
     }