get_source_slice produces segmentation fault when slice area is smaller than source area

[oskooi]

The get_source_slice routine produces a segmentation fault when the slice area is smaller than the source area. This is demonstrated in the following example of a source with a Gaussian spatial profile centered at the origin and defined by an amplitude function.

import meep as mp
import cmath
import numpy as np
import matplotlib.pyplot as plt

resolution = 50

cell_size = mp.Vector3(7,7,0)

def src_amp(x0):
  if x0.norm() < 2.0:
    return cmath.exp(-x0.norm()**2)
  else:
    return 0

sources = [mp.Source(mp.GaussianSource(1,fwidth=0.2),
                     component=mp.Ez,
                     center=mp.Vector3(),
                     size=mp.Vector3(4,4,0),
                     amp_func=src_amp)]

sim = mp.Simulation(resolution=resolution,
                    cell_size=cell_size,
                    k_point=mp.Vector3(),
                    sources=sources)

sim.init_sim()
src_data = sim.get_source_slice(mp.Ez, center=mp.Vector3(), size=mp.Vector3(6,6,0))

plt.figure(dpi=100)
plt.imshow(np.real(src_data.transpose()), cmap='hot_r', interpolation='spline36')
plt.axis('off')
plt.show()

For the case shown above in which the source area is of size mp.Vector3(4,4,0) and the slice area is mp.Vector3(6,6,0), the results are as expected:

However, when the area of the slice is strictly smaller then that of the source (e.g., mp.Vector3(3,3,0)), a segmentation fault is produced:

Using MPI version 3.1, 1 processes
-----------
Initializing structure...
Working in 2D dimensions.
Computational cell is 7 x 7 x 0 with resolution 50
time for set_epsilon = 0.103206 s
-----------
python3.5: malloc.c:2401: sysmalloc: Assertion `(old_top == initial_top (av) && old_size == 0) || ((unsigned long) (old_size) >= MINSIZE && prev_inuse (old_top) && ((unsigned long) old_end & (pagesize - 1)) == 0)' failed.
[simpetus:12112] *** Process received signal ***
[simpetus:12112] Signal: Aborted (6)
[simpetus:12112] Signal code:  (-6)
[simpetus:12112] [ 0] /lib/x86_64-linux-gnu/libpthread.so.0(+0x12890)[0x7f6932423890]
[simpetus:12112] [ 1] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0xc7)[0x7f693205ee97]
[simpetus:12112] [ 2] /lib/x86_64-linux-gnu/libc.so.6(abort+0x141)[0x7f6932060801]
[simpetus:12112] [ 3] /lib/x86_64-linux-gnu/libc.so.6(+0x93a91)[0x7f69320b3a91]
[simpetus:12112] [ 4] /lib/x86_64-linux-gnu/libc.so.6(+0x94ff0)[0x7f69320b4ff0]
[simpetus:12112] [ 5] /lib/x86_64-linux-gnu/libc.so.6(__libc_malloc+0x27d)[0x7f69320b72ed]
[simpetus:12112] [ 6] python3.5[0x59ce9a]
[simpetus:12112] [ 7] python3.5(PyDict_SetItem+0x2c7)[0x5a0897]
[simpetus:12112] [ 8] python3.5[0x5347b7]
[simpetus:12112] [ 9] python3.5(PyEval_EvalFrameEx+0x7cc4)[0x53e444]
[simpetus:12112] [10] python3.5[0x5401ef]
[simpetus:12112] [11] python3.5(PyEval_EvalFrameEx+0x50bf)[0x53b83f]
[simpetus:12112] [12] python3.5[0x53fc97]
[simpetus:12112] [13] python3.5(PyEval_EvalCode+0x1f)[0x5409bf]
[simpetus:12112] [14] python3.5[0x60cb42]
[simpetus:12112] [15] python3.5(PyRun_FileExFlags+0x9a)[0x60efea]
[simpetus:12112] [16] python3.5(PyRun_SimpleFileExFlags+0x1bc)[0x60f7dc]
[simpetus:12112] [17] python3.5(Py_Main+0x456)[0x640256]
[simpetus:12112] [18] python3.5(main+0xe1)[0x4d0001]
[simpetus:12112] [19] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7)[0x7f6932041b97]
[simpetus:12112] [20] python3.5(_start+0x29)[0x5d6999]
[simpetus:12112] *** End of error message ***
Aborted

It should be possible to define the source slice to have an area that is smaller than the overall source area.