Add a way to render the state

Note that this has exposed some scaling error that needs to be fixed.

examples/coremem.rs

@@ -1,5 +1,13 @@
 use coremem::SimState;
+use coremem::render::NumericTermRenderer;
+use std::{thread, time};
+
 fn main() {
-    let mut state = SimState::default();
+    let mut state = SimState::new(16);
-    state.step();
+    state.impulse_e(10, 1.0);
+    loop {
+        NumericTermRenderer.render(&state);
+        state.step();
+        thread::sleep(time::Duration::from_millis(500));
+    }
 }

src/lib.rs

@@ -5,6 +5,8 @@
 //!
 //! [1] https://www.eecs.wsu.edu/~schneidj/ufdtd/ufdtd.pdf
 
+pub mod render;
+
 // Some things to keep in mind:
 // B = mu_r*H + M
 // For a vacuum, B = H
@@ -24,8 +26,14 @@ pub struct SimState {
 }
 
 impl SimState {
+    pub fn new(size: usize) -> Self {
+        Self {
+            cells: vec![Cell::default(); size],
+        }
+    }
+
     pub fn step(&mut self) {
-        let mut working_cells = self.cells.clone();
+        let mut working_cells = vec![Cell::default(); self.cells.len()];
         // first advance all the magnetic fields
         for (i, left_cell) in self.cells.iter().enumerate() {
             let right_cell = match self.cells.get(i+1) {
@@ -43,7 +51,12 @@ impl SimState {
             self.cells[i] = right_cell.step_e(left_cell);
         }
     }
-    pub fn get(&self) -> &[Cell] {
+
+    pub fn impulse_e(&mut self, idx: usize, e: f32) {
+        self.cells[idx].ez += e;
+    }
+
+    pub fn cells(&self) -> &[Cell] {
         &*self.cells
     }
 }
@@ -66,6 +79,12 @@ pub struct Cell {
 }
 
 impl Cell {
+    pub fn ez(&self) -> f32 {
+        self.ez
+    }
+    pub fn by(&self) -> f32 {
+        self.by
+    }
     fn step_b(self, right: Cell) -> Self {
         // Maxwell's equation: del x E = -dB/dt
         // Expands: dB_y/dt = dE_z/dx

src/render.rs

@@ -0,0 +1,17 @@
+use crate::SimState;
+
+pub struct NumericTermRenderer;
+
+impl NumericTermRenderer {
+    pub fn render(&self, state: &SimState) {
+        print!("E:   ");
+        for cell in state.cells() {
+            print!("{:>8.1e} ", cell.ez());
+        }
+        print!("\nB:   ");
+        for cell in state.cells() {
+            print!("{:>8.1e} ", cell.by());
+        }
+        print!("\n");
+    }
+}