Air mass: Difference between revisions
Added Rust solution
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90 │ 34.32981136 34.36666557
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</pre>
=={{header|Rust}}==
{{trans|FreeBASIC}}
<lang rust>const RE: f64 = 6371000.0; // Earth radius in meters
const DD: f64 = 0.001; // integrate in this fraction of the distance already covered
const FIN: f64 = 10000000.0; // integrate only to a height of 10000km, effectively infinity
fn rho(a: f64) -> f64 {
// the density of air as a function of height above sea level
(-a / 8500.0).exp()
}
fn height(a: f64, z: f64, d: f64) -> f64 {
// a = altitude of observer
// z = zenith angle (in degrees)
// d = distance along line of sight
let aa = RE + a;
let hh = (aa * aa + d * d - 2.0 * d * aa * (180.0 - z).to_radians().cos()).sqrt();
hh - RE
}
fn column_density(a: f64, z: f64) -> f64 {
// integrates density along the line of sight
let mut sum = 0.0;
let mut d = 0.0;
while d < FIN {
// adaptive step size to avoid it taking forever
let mut delta = DD * d;
if delta < DD {
delta = DD;
}
sum += rho(height(a, z, d + 0.5 * delta)) * delta;
d += delta;
}
sum
}
fn airmass(a: f64, z: f64) -> f64 {
column_density(a, z) / column_density(a, 0.0)
}
fn main() {
println!("Angle 0 m 13700 m");
println!("------------------------------------");
for a in (0..=90).step_by(5) {
let z = a as f64;
println!(
"{:2} {:11.8} {:11.8}",
z,
airmass(0.0, z),
airmass(13700.0, z)
);
}
}</lang>
{{out}}
<pre>Angle 0 m 13700 m
------------------------------------
0 1.00000000 1.00000000
5 1.00380963 1.00380965
10 1.01538466 1.01538475
15 1.03517744 1.03517765
20 1.06399053 1.06399093
25 1.10305937 1.10306005
30 1.15418974 1.15419083
35 1.21998076 1.21998246
40 1.30418931 1.30419190
45 1.41234169 1.41234567
50 1.55280404 1.55281025
55 1.73875921 1.73876915
60 1.99212000 1.99213665
65 2.35199740 2.35202722
70 2.89531368 2.89537287
75 3.79582352 3.79596149
80 5.53885809 5.53928113
85 10.07896219 10.08115981
90 34.32981136 34.36666557
</pre>
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