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Update C++ implementations for Verlet algorithms #299

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Merged
merged 3 commits into from
Sep 14, 2018
Merged

Update C++ implementations for Verlet algorithms #299

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10ebadf
Adjust C++ code for Verlet according to #257
berquist Jul 24, 2018
fc192e2
use tie and swap typedef for using
berquist Aug 12, 2018
35365e8
keep results in a struct rather than a pair
berquist Aug 12, 2018
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52 changes: 37 additions & 15 deletions contents/verlet_integration/code/c++/verlet.cpp
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Original file line number Diff line number Diff line change
@@ -1,6 +1,11 @@
#include <iomanip>
#include <iostream>

// Simple function for velocity-verlet
struct timestep {
double time;
double vel;
};

double verlet(double pos, double acc, double dt) {

double prev_pos = pos;
Expand All @@ -16,8 +21,7 @@ double verlet(double pos, double acc, double dt) {
return time;
}

// Simple function for stormer-verlet
double stormer_verlet(double pos, double acc, double dt) {
timestep stormer_verlet(double pos, double acc, double dt) {

double prev_pos = pos;
double time = 0;
Expand All @@ -28,14 +32,15 @@ double stormer_verlet(double pos, double acc, double dt) {
prev_pos = pos;
pos = next_pos;

// The acceleration is constant, so the velocity is straightforward
// The acceleration is constant, so the velocity is
// straightforward
vel += acc * dt;
}

return time;
return timestep { time, vel };
}

double velocity_verlet(double pos, double acc, double dt) {
timestep velocity_verlet(double pos, double acc, double dt) {

double time = 0;
double vel = 0;
Expand All @@ -45,18 +50,35 @@ double velocity_verlet(double pos, double acc, double dt) {
vel += acc * dt;
}

return time;
return timestep { time, vel };
}

int main() {
std::cout << std::fixed << std::setprecision(8);

// Note that depending on the simulation, you might want to have the
// Verlet loop outside.

// For example, if your acceleration chages as a function of time,
// you might need to also change the acceleration to be read into
// each of these functions.

double time = verlet(5.0, -10, 0.01);
std::cout << "Time for Verlet integration is: " \
<< time << std::endl;

timestep timestep_sv = stormer_verlet(5.0, -10, 0.01);
std::cout << "Time for Stormer Verlet integration is: " \
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Why is there a backslash?

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I prefer to use an explicit line continuation indicator even when not required.

<< timestep_sv.time << std::endl;
std::cout << "Velocity for Stormer Verlet integration is: " \
<< timestep_sv.vel << std::endl;

timestep timestep_vv = velocity_verlet(5.0, -10, 0.01);
std::cout << "Time for velocity Verlet integration is: " \
<< timestep_vv.time << std::endl;
std::cout << "Velocity for velocity Verlet integration is: " \
<< timestep_vv.vel << std::endl;

// Note that depending on the simulation, you might want to have the verlet
// loop outside.
return 0;

// For example, if your acceleration chages as a function of time, you might
// need to also change the acceleration to be read into each of these
// functions
std::cout << verlet(5.0, -10, 0.01) << std::endl;
std::cout << stormer_verlet(5.0, -10, 0.01) << std::endl;
std::cout << velocity_verlet(5.0, -10, 0.01) << std::endl;
}
6 changes: 3 additions & 3 deletions contents/verlet_integration/verlet_integration.md
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Expand Up @@ -33,7 +33,7 @@ Here is what it looks like in code:
{% sample lang="jl" %}
[import:1-13, lang:"julia"](code/julia/verlet.jl)
{% sample lang="cpp" %}
[import:4-17, lang:"c_cpp"](code/c++/verlet.cpp)
[import:9-22, lang:"c_cpp"](code/c++/verlet.cpp)
{% sample lang="c" %}
[import:3-14, lang:"c_cpp"](code/c/verlet.c)
{% sample lang="java" %}
Expand Down Expand Up @@ -79,7 +79,7 @@ Here's what it looks like in code:
{% sample lang="jl" %}
[import:15-31, lang:"julia"](code/julia/verlet.jl)
{% sample lang="cpp" %}
[import:20-36, lang:"c_cpp"](code/c++/verlet.cpp)
[import:24-41, lang:"c_cpp"](code/c++/verlet.cpp)
{% sample lang="c" %}
[import:16-31, lang:"c_cpp"](code/c/verlet.c)
{% sample lang="java" %}
Expand Down Expand Up @@ -136,7 +136,7 @@ Here is the velocity Verlet method in code:
{% sample lang="jl" %}
[import:33-45, lang:"julia"](code/julia/verlet.jl)
{% sample lang="cpp" %}
[import:38-49, lang:"c_cpp"](code/c++/verlet.cpp)
[import:43-54, lang:"c_cpp"](code/c++/verlet.cpp)
{% sample lang="c" %}
[import:33-43, lang:"c_cpp"](code/c/verlet.c)
{% sample lang="java" %}
Expand Down