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- <main>
 
- <article id="content">
 
- <header>
 
- <h1 class="title"><code>acceleration</code> module</h1>
 
- </header>
 
- <section id="section-intro">
 
- <p>Defines the possible routines for computing the gravitational forces in the
 
- simulation.</p>
 
- <p>All the methods in these file require a position (n, 3) vector, a mass (n, )
 
- vector and an optional softening scale float.</p>
 
- <details class="source">
 
- <summary>Source code</summary>
 
- <pre><code class="python">"""Defines the possible routines for computing the gravitational forces in the
 
- simulation.
 
- All the methods in these file require a position (n, 3) vector, a mass (n, )
 
- vector and an optional softening scale float."""
 
- import ctypes
 
- import numpy.ctypeslib as ctl
 
- import numpy as np
 
- from numba import jit
 
- def bruteForce(r_vec, mass, soft=0.):
 
-     """Calculates the acceleration generated by a set of masses on themselves.
 
-        Complexity O(n*m) where n is the total number of masses and m is the
 
-        number of massive particles.
 
-     Parameters:
 
-         r_vec (array): list of particles positions.
 
-             Shape (n, 3) where n is the number of particles
 
-         mass (array): list of particles masses.
 
-             Shape (n,)
 
-         soft (float): characteristic plummer softening length scale
 
-     Returns:
 
-         forces (array): list of forces acting on each particle.
 
-             Shape (n, 3)
 
-     """
 
-     # Only calculate forces from massive particles
 
-     mask = mass!=0
 
-     massMassive = mass[mask]
 
-     rMassive_vec = r_vec[mask]
 
-     #  x m x 1 matrix (m = number of massive particles) for broadcasting
 
-     mass_mat = massMassive.reshape(1, -1, 1)
 
-     # Calculate displacements
 
-     # r_ten is the direction of the pairwise displacements. Shape (n, m, 3)
 
-     # r_mat is the absolute distance of the pairwise displacements. (n, m, 1)
 
-     r_ten = rMassive_vec.reshape(1, -1, 3) - r_vec.reshape(-1, 1, 3)
 
-     r_mat = np.linalg.norm(r_ten, axis=-1, keepdims=True)
 
-     # Avoid division by zeros
 
-     # $a = M / (r + \epsilon)^2$, where $\epsilon$ is the softening scale
 
-     # r_ten/r_mat gives the direction unit vector
 
-     accel = np.divide(r_ten * mass_mat/(r_mat+soft)**2, r_mat, 
 
-         where=r_ten.astype(bool), out=r_ten) # Reuse memory from r_ten
 
-     return accel.sum(axis=1) # Add all forces on each particle
 
- @jit(nopython=True) # Numba annotation
 
- def bruteForceNumba(r_vec, mass, soft=0.):
 
-     """Calculates the acceleration generated by a set of masses on themselves.
 
-     It is done in the same way as in bruteForce, but this
 
-     method is ran through Numba"""
 
-     mask = mass!=0
 
-     massMassive = mass[mask]
 
-     rMassive_vec = r_vec[mask]
 
-     mass_mat = massMassive.reshape(1, -1, 1)
 
-     r_ten = rMassive_vec.reshape(1, -1, 3) - r_vec.reshape(-1, 1, 3)
 
-     # Avoid np.linalg.norm to allow Numba optimizations
 
-     r_mat = np.sqrt(r_ten[:,:,0:1]**2 + r_ten[:,:,1:2]**2 + r_ten[:,:,2:3]**2)
 
-     r_mat = np.where(r_mat == 0, np.ones_like(r_mat), r_mat)
 
-     accel = r_ten/r_mat * mass_mat/(r_mat+soft)**2
 
-     return accel.sum(axis=1) # Add all forces in each particle
 
- @jit(nopython=True) # Numba annotation
 
- def bruteForceNumbaOptimized(r_vec, mass, soft=0.):
 
-     """Calculates the acceleration generated by a set of masses on themselves.
 
-     This is optimized for high performance with Numba. All massive particles
 
-     must appear first."""
 
-     accel = np.zeros_like(r_vec) 
 
-     # Use superposition to add all the contributions
 
-     n = r_vec.shape[0] # Number of particles
 
-     delta = np.zeros((3,)) # Only allocate this once
 
-     for i in range(n):
 
-         # Only consider pairs with at least one massive particle i
 
-         if mass[i] == 0: break
 
-         for j in range(i+1, n):
 
-             # Explicitely separate components for high performance
 
-             # i.e. do not do delta = r_vec[j] - r_vec[i]
 
-             # (The effect of this is VERY relevant (x10) and has to do with
 
-             # memory reallocation) Numba will vectorize the loops.
 
-             for k in range(3): delta[k] = r_vec[j,k] - r_vec[i,k]
 
-             r = np.sqrt(delta[0]*delta[0] + delta[1]*delta[1] + delta[2]*delta[2])
 
-             tripler = (r+soft)**2 * r
 
-             
 
-             # Compute acceleration on first particle
 
-             mr3inv = mass[i]/(tripler)
 
-             # Again, do NOT do accel[j] -= mr3inv * delta
 
-             for k in range(3): accel[j,k] -= mr3inv * delta[k]
 
-             
 
-             # Compute acceleration on second particle
 
-             # For pairs with one massless particle, no reaction force
 
-             if mass[j] == 0: break
 
-             # Otherwise, opposite direction (+)
 
-             mr3inv = mass[j]/(tripler)
 
-             for k in range(3): accel[i,k] += mr3inv * delta[k]
 
-     return accel
 
- # C++ interface, load library
 
- ACCLIB = None
 
- def loadCPPLib():
 
-     """Loads the C++ shared library to the global variable ACCLIB. Must be
 
-     called before using the library."""
 
-     global ACCLIB
 
-     ACCLIB = ctypes.CDLL('cpp/acclib.so')
 
-     # Define appropiate types for library functions
 
-     doublepp = np.ctypeslib.ndpointer(dtype=np.uintp) # double**
 
-     doublep = ctl.ndpointer(np.float64, flags='aligned, c_contiguous')#double*
 
-     # Check cpp/acclib.cpp for function signatures
 
-     ACCLIB.bruteForceCPP.argtypes = [doublepp, doublep, 
 
-         ctypes.c_int, ctypes.c_double]
 
-     ACCLIB.barnesHutCPP.argtypes = [doublepp, doublep, 
 
-         ctypes.c_int, ctypes.c_double, ctypes.c_double, 
 
-         ctypes.c_double, ctypes.c_double, ctypes.c_double]
 
- def bruteForceCPP(r_vec, m_vec, soft=0.):
 
-     """Calculates the acceleration generated by a set of masses on themselves.
 
-     This is ran in a shared C++ library through Brute Force (pairwise sums)
 
-     Massive particles must appear first."""
 
-     # Convert array to data required by C++ library
 
-     if ACCLIB is None: loadCPPLib() # Singleton pattern
 
-     # Change type to be appropiate for calling library
 
-     r_vec_c = (r_vec.ctypes.data + np.arange(r_vec.shape[0]) 
 
-         * r_vec.strides[0]).astype(np.uintp)
 
-     # Set return type as double*
 
-     ACCLIB.bruteForceCPP.restype = np.ctypeslib.ndpointer(dtype=np.float64, 
 
-         shape=(r_vec.shape[0]*3,))
 
-     # Call the C++ function: double* bruteForceCPP
 
-     accel =  ACCLIB.bruteForceCPP(r_vec_c, m_vec, r_vec.shape[0], soft)
 
-     # Change shape to get the expected Numpy array (n, 3)
 
-     accel.shape = (-1, 3)
 
-     return accel
 
- def barnesHutCPP(r_vec, m_vec, soft=0.):
 
-     """Calculates the acceleration generated by a set of masses on themselves.
 
-     This is ran in a shared C++ library using a BarnesHut tree"""
 
-     # Convert array to data required by C++ library
 
-     if ACCLIB is None: loadCPPLib() # Singleton pattern
 
-     # Change type to be appropiate for calling library
 
-     r_vec_c = (r_vec.ctypes.data + np.arange(r_vec.shape[0]) 
 
-         * r_vec.strides[0]).astype(np.uintp)
 
-     # Set return type as double*
 
-     ACCLIB.barnesHutCPP.restype = np.ctypeslib.ndpointer(dtype=np.float64, 
 
-         shape=(r_vec.shape[0]*3,))
 
-     # Explicitely pass the corner and size of the box for the top node
 
-     px, py, pz = np.min(r_vec, axis=0)
 
-     size = np.max(np.max(r_vec, axis=0) - np.min(r_vec, axis=0))
 
-     # Call the C++ function: double* barnesHutCPP
 
-     accel =  ACCLIB.barnesHutCPP(r_vec_c, m_vec, r_vec.shape[0], 
 
-         size, px, py, pz, soft)
 
-     # Change shape to get the expected Numpy array (n, 3)
 
-     accel.shape = (-1, 3)
 
-     return accel</code></pre>
 
- </details>
 
- </section>
 
- <section>
 
- </section>
 
- <section>
 
- </section>
 
- <section>
 
- <h2 class="section-title" id="header-functions">Functions</h2>
 
- <dl>
 
- <dt id="acceleration.barnesHutCPP"><code class="name flex">
 
- <span>def <span class="ident">barnesHutCPP</span></span>(<span>r_vec, m_vec, soft=0.0)</span>
 
- </code></dt>
 
- <dd>
 
- <section class="desc"><p>Calculates the acceleration generated by a set of masses on themselves.
 
- This is ran in a shared C++ library using a BarnesHut tree</p></section>
 
- <details class="source">
 
- <summary>Source code</summary>
 
- <pre><code class="python">def barnesHutCPP(r_vec, m_vec, soft=0.):
 
-     """Calculates the acceleration generated by a set of masses on themselves.
 
-     This is ran in a shared C++ library using a BarnesHut tree"""
 
-     # Convert array to data required by C++ library
 
-     if ACCLIB is None: loadCPPLib() # Singleton pattern
 
-     # Change type to be appropiate for calling library
 
-     r_vec_c = (r_vec.ctypes.data + np.arange(r_vec.shape[0]) 
 
-         * r_vec.strides[0]).astype(np.uintp)
 
-     # Set return type as double*
 
-     ACCLIB.barnesHutCPP.restype = np.ctypeslib.ndpointer(dtype=np.float64, 
 
-         shape=(r_vec.shape[0]*3,))
 
-     # Explicitely pass the corner and size of the box for the top node
 
-     px, py, pz = np.min(r_vec, axis=0)
 
-     size = np.max(np.max(r_vec, axis=0) - np.min(r_vec, axis=0))
 
-     # Call the C++ function: double* barnesHutCPP
 
-     accel =  ACCLIB.barnesHutCPP(r_vec_c, m_vec, r_vec.shape[0], 
 
-         size, px, py, pz, soft)
 
-     # Change shape to get the expected Numpy array (n, 3)
 
-     accel.shape = (-1, 3)
 
-     return accel</code></pre>
 
- </details>
 
- </dd>
 
- <dt id="acceleration.bruteForce"><code class="name flex">
 
- <span>def <span class="ident">bruteForce</span></span>(<span>r_vec, mass, soft=0.0)</span>
 
- </code></dt>
 
- <dd>
 
- <section class="desc"><p>Calculates the acceleration generated by a set of masses on themselves.
 
- Complexity O(n*m) where n is the total number of masses and m is the
 
- number of massive particles.</p>
 
- <h2 id="parameters">Parameters</h2>
 
- <dl>
 
- <dt><strong><code>r_vec</code></strong> : <code>array</code></dt>
 
- <dd>list of particles positions.
 
- Shape (n, 3) where n is the number of particles</dd>
 
- <dt><strong><code>mass</code></strong> : <code>array</code></dt>
 
- <dd>list of particles masses.
 
- Shape (n,)</dd>
 
- <dt><strong><code>soft</code></strong> : <code>float</code></dt>
 
- <dd>characteristic plummer softening length scale</dd>
 
- </dl>
 
- <h2 id="returns">Returns</h2>
 
- <dl>
 
- <dt><strong><code>forces</code></strong> : <code>array</code></dt>
 
- <dd>list of forces acting on each particle.
 
- Shape (n, 3)</dd>
 
- </dl></section>
 
- <details class="source">
 
- <summary>Source code</summary>
 
- <pre><code class="python">def bruteForce(r_vec, mass, soft=0.):
 
-     """Calculates the acceleration generated by a set of masses on themselves.
 
-        Complexity O(n*m) where n is the total number of masses and m is the
 
-        number of massive particles.
 
-     Parameters:
 
-         r_vec (array): list of particles positions.
 
-             Shape (n, 3) where n is the number of particles
 
-         mass (array): list of particles masses.
 
-             Shape (n,)
 
-         soft (float): characteristic plummer softening length scale
 
-     Returns:
 
-         forces (array): list of forces acting on each particle.
 
-             Shape (n, 3)
 
-     """
 
-     # Only calculate forces from massive particles
 
-     mask = mass!=0
 
-     massMassive = mass[mask]
 
-     rMassive_vec = r_vec[mask]
 
-     #  x m x 1 matrix (m = number of massive particles) for broadcasting
 
-     mass_mat = massMassive.reshape(1, -1, 1)
 
-     # Calculate displacements
 
-     # r_ten is the direction of the pairwise displacements. Shape (n, m, 3)
 
-     # r_mat is the absolute distance of the pairwise displacements. (n, m, 1)
 
-     r_ten = rMassive_vec.reshape(1, -1, 3) - r_vec.reshape(-1, 1, 3)
 
-     r_mat = np.linalg.norm(r_ten, axis=-1, keepdims=True)
 
-     # Avoid division by zeros
 
-     # $a = M / (r + \epsilon)^2$, where $\epsilon$ is the softening scale
 
-     # r_ten/r_mat gives the direction unit vector
 
-     accel = np.divide(r_ten * mass_mat/(r_mat+soft)**2, r_mat, 
 
-         where=r_ten.astype(bool), out=r_ten) # Reuse memory from r_ten
 
-     return accel.sum(axis=1) # Add all forces on each particle</code></pre>
 
- </details>
 
- </dd>
 
- <dt id="acceleration.bruteForceCPP"><code class="name flex">
 
- <span>def <span class="ident">bruteForceCPP</span></span>(<span>r_vec, m_vec, soft=0.0)</span>
 
- </code></dt>
 
- <dd>
 
- <section class="desc"><p>Calculates the acceleration generated by a set of masses on themselves.
 
- This is ran in a shared C++ library through Brute Force (pairwise sums)
 
- Massive particles must appear first.</p></section>
 
- <details class="source">
 
- <summary>Source code</summary>
 
- <pre><code class="python">def bruteForceCPP(r_vec, m_vec, soft=0.):
 
-     """Calculates the acceleration generated by a set of masses on themselves.
 
-     This is ran in a shared C++ library through Brute Force (pairwise sums)
 
-     Massive particles must appear first."""
 
-     # Convert array to data required by C++ library
 
-     if ACCLIB is None: loadCPPLib() # Singleton pattern
 
-     # Change type to be appropiate for calling library
 
-     r_vec_c = (r_vec.ctypes.data + np.arange(r_vec.shape[0]) 
 
-         * r_vec.strides[0]).astype(np.uintp)
 
-     # Set return type as double*
 
-     ACCLIB.bruteForceCPP.restype = np.ctypeslib.ndpointer(dtype=np.float64, 
 
-         shape=(r_vec.shape[0]*3,))
 
-     # Call the C++ function: double* bruteForceCPP
 
-     accel =  ACCLIB.bruteForceCPP(r_vec_c, m_vec, r_vec.shape[0], soft)
 
-     # Change shape to get the expected Numpy array (n, 3)
 
-     accel.shape = (-1, 3)
 
-     return accel</code></pre>
 
- </details>
 
- </dd>
 
- <dt id="acceleration.bruteForceNumba"><code class="name flex">
 
- <span>def <span class="ident">bruteForceNumba</span></span>(<span>r_vec, mass, soft=0.0)</span>
 
- </code></dt>
 
- <dd>
 
- <section class="desc"><p>Calculates the acceleration generated by a set of masses on themselves.
 
- It is done in the same way as in bruteForce, but this
 
- method is ran through Numba</p></section>
 
- <details class="source">
 
- <summary>Source code</summary>
 
- <pre><code class="python">@jit(nopython=True) # Numba annotation
 
- def bruteForceNumba(r_vec, mass, soft=0.):
 
-     """Calculates the acceleration generated by a set of masses on themselves.
 
-     It is done in the same way as in bruteForce, but this
 
-     method is ran through Numba"""
 
-     mask = mass!=0
 
-     massMassive = mass[mask]
 
-     rMassive_vec = r_vec[mask]
 
-     mass_mat = massMassive.reshape(1, -1, 1)
 
-     r_ten = rMassive_vec.reshape(1, -1, 3) - r_vec.reshape(-1, 1, 3)
 
-     # Avoid np.linalg.norm to allow Numba optimizations
 
-     r_mat = np.sqrt(r_ten[:,:,0:1]**2 + r_ten[:,:,1:2]**2 + r_ten[:,:,2:3]**2)
 
-     r_mat = np.where(r_mat == 0, np.ones_like(r_mat), r_mat)
 
-     accel = r_ten/r_mat * mass_mat/(r_mat+soft)**2
 
-     return accel.sum(axis=1) # Add all forces in each particle</code></pre>
 
- </details>
 
- </dd>
 
- <dt id="acceleration.bruteForceNumbaOptimized"><code class="name flex">
 
- <span>def <span class="ident">bruteForceNumbaOptimized</span></span>(<span>r_vec, mass, soft=0.0)</span>
 
- </code></dt>
 
- <dd>
 
- <section class="desc"><p>Calculates the acceleration generated by a set of masses on themselves.
 
- This is optimized for high performance with Numba. All massive particles
 
- must appear first.</p></section>
 
- <details class="source">
 
- <summary>Source code</summary>
 
- <pre><code class="python">@jit(nopython=True) # Numba annotation
 
- def bruteForceNumbaOptimized(r_vec, mass, soft=0.):
 
-     """Calculates the acceleration generated by a set of masses on themselves.
 
-     This is optimized for high performance with Numba. All massive particles
 
-     must appear first."""
 
-     accel = np.zeros_like(r_vec) 
 
-     # Use superposition to add all the contributions
 
-     n = r_vec.shape[0] # Number of particles
 
-     delta = np.zeros((3,)) # Only allocate this once
 
-     for i in range(n):
 
-         # Only consider pairs with at least one massive particle i
 
-         if mass[i] == 0: break
 
-         for j in range(i+1, n):
 
-             # Explicitely separate components for high performance
 
-             # i.e. do not do delta = r_vec[j] - r_vec[i]
 
-             # (The effect of this is VERY relevant (x10) and has to do with
 
-             # memory reallocation) Numba will vectorize the loops.
 
-             for k in range(3): delta[k] = r_vec[j,k] - r_vec[i,k]
 
-             r = np.sqrt(delta[0]*delta[0] + delta[1]*delta[1] + delta[2]*delta[2])
 
-             tripler = (r+soft)**2 * r
 
-             
 
-             # Compute acceleration on first particle
 
-             mr3inv = mass[i]/(tripler)
 
-             # Again, do NOT do accel[j] -= mr3inv * delta
 
-             for k in range(3): accel[j,k] -= mr3inv * delta[k]
 
-             
 
-             # Compute acceleration on second particle
 
-             # For pairs with one massless particle, no reaction force
 
-             if mass[j] == 0: break
 
-             # Otherwise, opposite direction (+)
 
-             mr3inv = mass[j]/(tripler)
 
-             for k in range(3): accel[i,k] += mr3inv * delta[k]
 
-     return accel</code></pre>
 
- </details>
 
- </dd>
 
- <dt id="acceleration.loadCPPLib"><code class="name flex">
 
- <span>def <span class="ident">loadCPPLib</span></span>(<span>)</span>
 
- </code></dt>
 
- <dd>
 
- <section class="desc"><p>Loads the C++ shared library to the global variable ACCLIB. Must be
 
- called before using the library.</p></section>
 
- <details class="source">
 
- <summary>Source code</summary>
 
- <pre><code class="python">def loadCPPLib():
 
-     """Loads the C++ shared library to the global variable ACCLIB. Must be
 
-     called before using the library."""
 
-     global ACCLIB
 
-     ACCLIB = ctypes.CDLL('cpp/acclib.so')
 
-     # Define appropiate types for library functions
 
-     doublepp = np.ctypeslib.ndpointer(dtype=np.uintp) # double**
 
-     doublep = ctl.ndpointer(np.float64, flags='aligned, c_contiguous')#double*
 
-     # Check cpp/acclib.cpp for function signatures
 
-     ACCLIB.bruteForceCPP.argtypes = [doublepp, doublep, 
 
-         ctypes.c_int, ctypes.c_double]
 
-     ACCLIB.barnesHutCPP.argtypes = [doublepp, doublep, 
 
-         ctypes.c_int, ctypes.c_double, ctypes.c_double, 
 
-         ctypes.c_double, ctypes.c_double, ctypes.c_double]</code></pre>
 
- </details>
 
- </dd>
 
- </dl>
 
- </section>
 
- <section>
 
- </section>
 
- </article>
 
- <nav id="sidebar">
 
- <h1>Index</h1>
 
- <div class="toc">
 
- <ul></ul>
 
- </div>
 
- <ul id="index">
 
- <li><h3><a href="#header-functions">Functions</a></h3>
 
- <ul class="">
 
- <li><code><a title="acceleration.barnesHutCPP" href="#acceleration.barnesHutCPP">barnesHutCPP</a></code></li>
 
- <li><code><a title="acceleration.bruteForce" href="#acceleration.bruteForce">bruteForce</a></code></li>
 
- <li><code><a title="acceleration.bruteForceCPP" href="#acceleration.bruteForceCPP">bruteForceCPP</a></code></li>
 
- <li><code><a title="acceleration.bruteForceNumba" href="#acceleration.bruteForceNumba">bruteForceNumba</a></code></li>
 
- <li><code><a title="acceleration.bruteForceNumbaOptimized" href="#acceleration.bruteForceNumbaOptimized">bruteForceNumbaOptimized</a></code></li>
 
- <li><code><a title="acceleration.loadCPPLib" href="#acceleration.loadCPPLib">loadCPPLib</a></code></li>
 
- </ul>
 
- </li>
 
- </ul>
 
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