some fixes and updates

src/density_z.rs

@@ -0,0 +1,97 @@
+mod trajectory;
+use trajectory::*;
+use std::env;
+
+fn main() {
+    // open file
+    let args: Vec<String> = env::args().collect();
+
+    let mut filename : String = "montecarlo.xyz".to_string();
+    let mut skip_frames : usize = 0;
+    let mut slabs : usize = 256;
+    for i in 0..args.len() {
+        if args[i] == "-f" {
+            filename = args[i+1].clone();
+        } else if args[i] == "-s" {
+            skip_frames = args[i+1].parse::<usize>().unwrap();
+        } else if args[i] == "--slabs" {
+            slabs = args[i+1].parse::<usize>().unwrap();
+        }
+    }
+
+    let mut trj_reader = TrjReader::new(&filename);
+
+    // skip some frames
+    println!("# Skipping {} frames.", skip_frames);
+    trj_reader.skip(skip_frames);
+    let mut frame = trj_reader.next_frame();
+
+    let slab_height = frame.box_z / slabs as f64;
+    let slab_volume = slab_height * frame.box_x * frame.box_y;
+    println!("# Density calculation with {} slabs (height={})", slabs, slab_height);
+
+    let mut slab_particles : Vec<f64> = vec![0.0; slabs];
+    let mut frame_count : usize = 0;
+
+    // loop over frames
+    loop  {
+        frame_count += 1;
+        for i in 0..frame.num_particles {
+            let slab_no : usize = get_slab_number_for_position(frame.rz[i], slab_height) - 1;
+            slab_particles[slab_no] += 1.0;
+        }
+
+        if !trj_reader.update_with_next(&mut frame) {
+            break;
+        }
+    }
+
+    println!("# Averaged over {} frames", frame_count);
+    println!("# Position    Density");
+    for i in 0..slab_particles.len() {
+        let p_max = slab_height * (i as f64 + 1.0);
+        let position =(p_max + p_max-slab_height) / 2.0;
+        let particles = slab_particles[i] / frame_count as f64;
+        let density = particles / slab_volume;
+        println!("{}\t{}\t{}", position, density, particles);
+    }
+
+}
+
+pub fn get_slab_number_for_position(z: f64, slab_height: f64) -> usize {
+    let mut slab = 0;
+    let mut z_counter = 0.0_f64;
+    while z_counter  <= z {
+        z_counter += slab_height;
+        slab += 1;
+    }
+    return slab;
+}
+
+#[test]
+fn test_get_slab_no() {
+    let z = 3.5;
+    let slab_height = 1.0;
+    assert_eq!(4, get_slab_number_for_position(z, slab_height));
+
+    let z = 0.0;
+    let slab_height = 1.0;
+    assert_eq!(1, get_slab_number_for_position(z, slab_height));
+
+    let z = 0.1;
+    let slab_height = 0.2;
+    assert_eq!(1, get_slab_number_for_position(z, slab_height));
+
+    let z = 0.0001;
+    let slab_height = 0.2;
+    assert_eq!(1, get_slab_number_for_position(z, slab_height));
+
+
+    let z = 0.19999999_f64;
+    let slab_height = 0.2;
+    assert_eq!(1, get_slab_number_for_position(z, slab_height));
+
+    let z = 1.0;
+    let slab_height = 1.0;
+    assert_eq!(2, get_slab_number_for_position(z, slab_height));
+}