Orbital elements: Difference between revisions
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TODO: pick an example from a reputable source, and bring the algorithm description onto this site. (Restating those pages in concise a fashion comprehensible to the coders and readers of this site will be a good exercise.)
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=={{header|C}}==
{{trans|Kotlin}}
<lang c>#include <stdio.h>
#include <math.h>
typedef struct {
double x, y, z;
} vector;
vector add(vector v, vector w) {
return (vector){v.x + w.x, v.y + w.y, v.z + w.z};
}
vector mul(vector v, double m) {
return (vector){v.x * m, v.y * m, v.z * m};
}
vector div(vector v, double d) {
return mul(v, 1.0 / d);
}
double vabs(vector v) {
return sqrt(v.x * v.x + v.y * v.y + v.z * v.z);
}
vector mulAdd(vector v1, vector v2, double x1, double x2) {
return add(mul(v1, x1), mul(v2, x2));
}
void vecAsStr(char buffer[], vector v) {
sprintf(buffer, "(%.17g, %.17g, %.17g)", v.x, v.y, v.z);
}
void rotate(vector i, vector j, double alpha, vector ps[]) {
ps[0] = mulAdd(i, j, cos(alpha), sin(alpha));
ps[1] = mulAdd(i, j, -sin(alpha), cos(alpha));
}
void orbitalStateVectors(
double semimajorAxis, double eccentricity, double inclination,
double longitudeOfAscendingNode, double argumentOfPeriapsis,
double trueAnomaly, vector ps[]) {
vector i = {1.0, 0.0, 0.0};
vector j = {0.0, 1.0, 0.0};
vector k = {0.0, 0.0, 1.0};
double l = 2.0, c, s, r, rprime;
vector qs[2];
rotate(i, j, longitudeOfAscendingNode, qs);
i = qs[0]; j = qs[1];
rotate(j, k, inclination, qs);
j = qs[0];
rotate(i, j, argumentOfPeriapsis, qs);
i = qs[0]; j = qs[1];
if (eccentricity != 1.0) l = 1.0 - eccentricity * eccentricity;
l *= semimajorAxis;
c = cos(trueAnomaly);
s = sin(trueAnomaly);
r = l / (1.0 + eccentricity * c);
rprime = s * r * r / l;
ps[0] = mulAdd(i, j, c, s);
ps[0] = mul(ps[0], r);
ps[1] = mulAdd(i, j, rprime * c - r * s, rprime * s + r * c);
ps[1] = div(ps[1], vabs(ps[1]));
ps[1] = mul(ps[1], sqrt(2.0 / r - 1.0 / semimajorAxis));
}
int main() {
double longitude = 355.0 / (113.0 * 6.0);
vector ps[2];
char buffer[80];
orbitalStateVectors(1.0, 0.1, 0.0, longitude, 0.0, 0.0, ps);
vecAsStr(buffer, ps[0]);
printf("Position : %s\n", buffer);
vecAsStr(buffer, ps[1]);
printf("Speed : %s\n", buffer);
return 0;
}</lang>
{{output}}
<pre>
Position : (0.77942284339867973, 0.45000003465368416, 0)
Speed : (-0.55277084096044382, 0.95742708317976177, 0)
</pre>
=={{header|D}}==
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