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84 lines
3.6 KiB
Java
84 lines
3.6 KiB
Java
package com.thealgorithms.physics;
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import static org.junit.jupiter.api.Assertions.assertArrayEquals;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import org.junit.jupiter.api.DisplayName;
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import org.junit.jupiter.api.Test;
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/**
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* Unit tests for the Gravitation utility class.
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*/
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final class GravitationTest {
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// A small tolerance (delta) for comparing floating-point numbers
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private static final double DELTA = 1e-9;
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private static final double G = Gravitation.GRAVITATIONAL_CONSTANT;
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@Test
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@DisplayName("Test gravitational force between two bodies on the x-axis")
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void testSimpleForceCalculation() {
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// Force on body 2 should be F = G*1*1 / 1^2 = G, directed towards body 1 (negative x)
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double[] forceOnB = Gravitation.calculateGravitationalForce(1.0, 0, 0, 1.0, 1, 0);
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assertArrayEquals(new double[] {-G, 0.0}, forceOnB, DELTA);
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// Force on body 1 should be equal and opposite (positive x)
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double[] forceOnA = Gravitation.calculateGravitationalForce(1.0, 1, 0, 1.0, 0, 0);
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assertArrayEquals(new double[] {G, 0.0}, forceOnA, DELTA);
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}
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@Test
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@DisplayName("Test gravitational force in a 2D plane")
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void test2DForceCalculation() {
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// Body 1 at (0,0) with mass 2kg
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// Body 2 at (3,4) with mass 1kg
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// Distance is sqrt(3^2 + 4^2) = 5 meters
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double magnitude = 2.0 * G / 25.0; // G * 2 * 1 / 5^2
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// Unit vector from 2 to 1 is (-3/5, -4/5)
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double expectedFx = magnitude * -3.0 / 5.0; // -6G / 125
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double expectedFy = magnitude * -4.0 / 5.0; // -8G / 125
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double[] forceOnB = Gravitation.calculateGravitationalForce(2.0, 0, 0, 1.0, 3, 4);
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assertArrayEquals(new double[] {expectedFx, expectedFy}, forceOnB, DELTA);
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}
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@Test
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@DisplayName("Test overlapping bodies should result in zero force")
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void testOverlappingBodies() {
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double[] force = Gravitation.calculateGravitationalForce(1000.0, 1.5, -2.5, 500.0, 1.5, -2.5);
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assertArrayEquals(new double[] {0.0, 0.0}, force, DELTA);
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}
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@Test
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@DisplayName("Test circular orbit velocity with simple values")
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void testCircularOrbitVelocity() {
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// v = sqrt(G*1/1) = sqrt(G)
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double velocity = Gravitation.calculateCircularOrbitVelocity(1.0, 1.0);
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assertEquals(Math.sqrt(G), velocity, DELTA);
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}
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@Test
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@DisplayName("Test orbital velocity with real-world-ish values (LEO)")
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void testEarthOrbitVelocity() {
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// Mass of Earth ~5.972e24 kg
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// Radius of LEO ~6,771,000 m (Earth radius + 400km)
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double earthMass = 5.972e24;
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double leoRadius = 6.771e6;
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// FIX: Updated expected value to match the high-precision calculation
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double expectedVelocity = 7672.4904;
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double velocity = Gravitation.calculateCircularOrbitVelocity(earthMass, leoRadius);
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assertEquals(expectedVelocity, velocity, 0.0001); // Use a larger delta for big numbers
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}
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@Test
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@DisplayName("Test invalid inputs for orbital velocity throw exception")
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void testInvalidOrbitalVelocityInputs() {
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assertThrows(IllegalArgumentException.class, () -> Gravitation.calculateCircularOrbitVelocity(0, 100));
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assertThrows(IllegalArgumentException.class, () -> Gravitation.calculateCircularOrbitVelocity(-1000, 100));
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assertThrows(IllegalArgumentException.class, () -> Gravitation.calculateCircularOrbitVelocity(1000, 0));
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assertThrows(IllegalArgumentException.class, () -> Gravitation.calculateCircularOrbitVelocity(1000, -100));
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}
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}
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