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	tadd simulation parameter value check - slidergrid - grid of elastic sliders on…
	git clone git://src.adamsgaard.dk/slidergrid
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	---
	commit abf7d095f654ff0108832d8055a3ce72bf333920
	parent d71a34ad2042f7d67856a76cc130c204a69a3550
	Author: Anders Damsgaard <[email protected]>
	Date: Wed, 16 Mar 2016 13:01:36 -0700

	add simulation parameter value check

	Diffstat:
	M main.c \| 12 +++++++++---
	M simulation.c \| 63 +++++++++++++++++++++++++++++…
	M simulation.h \| 9 +++++----
	M slider.c \| 6 +++---
	M slider.h \| 4 ----

	5 files changed, 77 insertions(+), 17 deletions(-)
	---
	diff --git a/main.c b/main.c
	t@@ -23,6 +23,8 @@ simulation setup_simulation()
	sim.sliders[i].mass = 1.;
	sim.sliders[i].moment_of_inertia = 1.;
	}
	+
	+ return sim;
	}

	int main(int argc, char** argv)
	t@@ -40,16 +42,20 @@ int main(int argc, char** argv)
	find_and_bond_to_neighbors_n2(sim.sliders, sim.N, sim.bond_length_limit);

	// determine time step length
	- sim.dt = find_time_step(sim.sliders, sim.N);
	+ sim.dt = find_time_step(sim.sliders, sim.N, 0.07);

	// check simulation parameters for missing or wrong parameter values
	- if (check_simulation(sim)) {
	+ if (check_simulation_values(sim)) {
	fprintf(stderr, "Error: Simulation configuration invalid.\n");
	return EXIT_FAILURE;
	}

	// temporal loop
	- for (sim.t=0.0; sim.t<=sim.t_end; sim.t+=sim.dt) {
	+ sim.iteration = 0;
	+ for (sim.time = 0.0;
	+ sim.time <= sim.time_end;
	+ sim.time += sim.dt) {
	+
	for (i=0; i<sim.N; i++) {
	update_kinematics(sim.sliders[i], sim.dt, sim.iteration);
	}
	diff --git a/simulation.c b/simulation.c
	t@@ -1,16 +1,73 @@
	+#include <stdio.h>
	+#include <math.h>
	#include "slider.h"
	#include "simulation.h"

	int check_simulation_values(const simulation sim)
	{
	+ int return_status = 0;

	+ // Slider-specific parameters
	+ int i;
	+ for (i=0; i<sim.N; i++) {

	+ if (sim.sliders[i].mass <= 0.0) {
	+ fprintf(stderr, "Error: Mass of slider %d is zero or negative "
	+ "(%f kg)\n", i, sim.sliders[i].mass);
	+ return_status = 1;
	+ }
	+
	+ if (sim.sliders[i].moment_of_inertia <= 0.0) {
	+ fprintf(stderr, "Error: Moment of inertia of slider %d is "
	+ "zero or negative (%f kgmm)\n",
	+ i, sim.sliders[i].moment_of_inertia);
	+ return_status = 1;
	+ }
	+ }
	+
	+ // General parameters
	+ if (sim.N <= 0) {
	+ fprintf(stderr, "Error: The number of sliders (N = %d) must be a "
	+ "positive number.\n", sim.N);
	+ return_status = 1;
	+ }
	+
	+ if (sim.dt <= 0.0) {
	+ fprintf(stderr, "Error: The numerical time step (dt = %f) must be a "
	+ "positive value.\n", sim.dt);
	+ return_status = 1;
	+ }
	+
	+ if (sim.time > sim.time_end) {
	+ fprintf(stderr, "Error: Current time (time = %f s) exceeds "
	+ "total time (time_end = %f s)\n",
	+ sim.time, sim.time_end);
	+ return_status = 1;
	+ }
	+
	+ if (sim.bond_length_limit <= 0.0) {
	+ fprintf(stderr, "Error: The inter-slider bond length limit "
	+ "(bond_length_limit = %f) must be a positive value.\n",
	+ sim.bond_length_limit);
	+ return_status = 1;
	+ }
	+
	+
	+ return return_status;
	}

	-Float find_time_step(const slider* sliders, const int N)
	+Float find_time_step(const slider* sliders, const int N, const Float safety)
	{
	- Float largest_dt = 0.;
	+ Float smallest_mass = 1.0e20;
	+ Float largest_stiffness = 0.0;

	+ int i;
	+ for (i=0; i<N; i++) {
	+ if (sliders[i].mass < smallest_mass)
	+ smallest_mass = sliders[i].mass;
	+ if (sliders[i].bond_parallel_stiffness > largest_stiffness)
	+ largest_stiffness = sliders[i].bond_parallel_stiffness;
	+ }

	- return largest_dt;
	+ return safety/sqrt(largest_stiffness/smallest_mass);
	}
	diff --git a/simulation.h b/simulation.h
	t@@ -4,16 +4,17 @@
	typedef struct {
	slider* sliders;
	int N;
	- Float t;
	- Float t_end;
	+ Float time;
	+ Float time_end;
	Float dt;
	long int iteration;
	Float bond_length_limit;

	} simulation;

	-Float find_time_step(const slider* sim.sliders, const int sim.N);
	-int check_simulation(const simulation sim);
	+Float find_time_step(const slider* sliders, const int N, const Float safety);
	+
	+int check_simulation_values(const simulation sim);

	// user-defined function which sets up the simulation
	simulation setup_simulation();
	diff --git a/slider.c b/slider.c
	t@@ -17,9 +17,9 @@ void initialize_slider_values(slider s)
	int i;
	for (i=0; i<MAX_NEIGHBORS; i++) {
	s.neighbors[i] = -1;
	- s.neighbor_distance[i] = zeros_float3();
	- s.neighbor_relative_distance_displacement[i] = zeros_float3();
	- s.neighbor_relative_distance_velocity[i] = zeros_float3();
	+ s.neighbor_distance[i] = zeroes_float3();
	+ s.neighbor_relative_distance_displacement[i] = zeroes_float3();
	+ s.neighbor_relative_distance_velocity[i] = zeroes_float3();
	}

	}
	diff --git a/slider.h b/slider.h
	t@@ -33,10 +33,6 @@ typedef struct {
	Float bond_parallel_stiffness; // Hookean elastic stiffness [N/m]
	Float bond_parallel_viscosity; // viscosity [N/(m*s)]

	- // slider-surface contact model parameters
	- // should this value belong to the lower surface instead?
	- Float coulomb_friction; // Coulomb frictional value [-]
	-
	// The uniquely identifying indexes of the slider neighbors which are bond…
	// to this slider. A value of -1 denotes an empty field. Preallocated fo…
	// speed.