Corrected bug with looking for excitation file in same directory as input file.

docs/source/input.rst

@@ -666,7 +666,7 @@ If there are less amplitude values than the number of iterations that are going
 
     #excitation_file: file1
 
-``str1`` is the name of the ASCII file containing the specified waveform. It should be located in the same directory as the input file.
+``str1`` is the name (and optionally full path) of the ASCII file containing the specified waveform. ``str1`` will first be tested as the full path to the file, and if it does not exist it will look for ``str1`` in the same directory as the input file.
 
 For example, to specify the file ``my_waves.txt``, which contains two custom waveform shapes, use: ``#excitation_file: my_waves.txt``. The contents of the file ``my_waves.txt`` would take the form:
 

gprMax/input_cmds_singleuse.py

@@ -221,7 +221,11 @@ def process_singlecmds(singlecmds, multicmds, G):
             raise CmdInputError(cmd + ' requires exactly one parameter')
         excitationfile = tmp[0]
 
-        # Open file and get waveform names
+        # See if file exists at specified path and if not try input file directory
+        if not os.path.isfile(excitationfile):
+            excitationfile = os.path.join(G.inputdirectory, excitationfile)
+
+        # Get waveform names
         with open(excitationfile, 'r') as f:
             waveformIDs = f.readline().split()