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	tadd sphere volume device function and linear weighting function - sphere - GPU…
	git clone git://src.adamsgaard.dk/sphere
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	---
	commit d91d2b6dfe2aeff630816a5d527690c7747d9797
	parent fbf7ff188ee3c9616021d31a1cd3c77915240f39
	Author: Anders Damsgaard <[email protected]>
	Date: Thu, 19 Mar 2015 13:21:55 +0100

	add sphere volume device function and linear weighting function

	Diffstat:
	M src/darcy.cuh \| 35 +++++++++++++++++++++++++++--…

	1 file changed, 31 insertions(+), 4 deletions(-)
	---
	diff --git a/src/darcy.cuh b/src/darcy.cuh
	t@@ -265,6 +265,33 @@ __global__ void findDarcyParticleVelocities(
	}
	*/

	+// Return the volume of a sphere with radius r
	+__device__ Float sphereVolume(const Float r)
	+{
	+ if (r > 0.0)
	+ return 4.0/3.0M_PIpow(r, 3);
	+ else {
	+ printf("Error: Negative radius\n");
	+ return NAN;
	+ }
	+}
	+
	+// Returns a weighting factor based on particle position and fluid center
	+// position
	+__device__ Float weight(
	+ const Float3 x_p, // in: Particle center position
	+ const Float3 x_f, // in: Fluid pressure node position
	+ const Float dx, // in: Cell spacing, x
	+ const Float dy, // in: Cell spacing, y
	+ const Float dz) // in: Cell spacing, z
	+{
	+ const Float x_len = length(x_p - x_f);
	+ if (x_len.x < dx && x_len.y < dy && x_len.z < dz)
	+ return (1.0 - x_len.x/dx)(1.0 - x_len.y/dy)(1.0 - x_len.z/dz);
	+ else
	+ return 0.0;
	+}
	+
	// Find the porosity in each cell on the base of a sphere, centered at the cell
	// center.
	__global__ void findDarcyPorosities(
	t@@ -300,7 +327,7 @@ __global__ void findDarcyPorosities(
	// Cell sphere radius
	const Float R = fmin(dx, fmin(dy,dz)) * 0.5; // diameter = cell width
	//const Float R = fmin(dx, fmin(dy,dz)); // diameter = 2*cell width
	- const Float cell_volume = 4.0/3.0M_PIRRR;
	+ const Float cell_volume = sphereVolume(R);

	Float void_volume = cell_volume; // current void volume
	Float void_volume_new = cell_volume; // projected new void volume
	t@@ -395,7 +422,7 @@ __global__ void findDarcyPorosities(

	// Particle fully contained in cell sphere
	if (d <= R - r)
	- void_volume -= 4.0/3.0M_PIrrr;
	+ void_volume -= sphereVolume(r);

	//// Find projected new void volume
	// Eulerian update of positions
	t@@ -420,7 +447,7 @@ __global__ void findDarcyPorosities(

	// Particle fully contained in cell sphere
	if (d <= R - r)
	- void_volume_new -= 4.0/3.0M_PIrrr;
	+ void_volume_new -= sphereVolume(r);
	}
	}
	}
	t@@ -608,7 +635,7 @@ __global__ void findDarcyPressureForce(
	//p_zp = p_zn;*/

	// find particle volume (radius in x.w)
	- const Float V = 4.0/3.0M_PIx.wx.wx.w;
	+ const Float V = sphereVolume(x.w);

	// determine pressure gradient from first order central difference
	const Float3 grad_p = MAKE_FLOAT3(