allow start file to be specified for mcmc samplers (gwastro#3394)

pycbc/inference/io/base_hdf.py

@@ -661,6 +661,8 @@ def copy_samples(self, other, parameters=None, parameter_names=None,
         # if list of desired parameters is different, rename
         if set(parameters) != set(self.variable_params):
             other.attrs['variable_params'] = parameters
+        if read_args is None:
+            read_args = {}
         samples = self.read_samples(parameters, **read_args)
         logging.info("Copying {} samples".format(samples.size))
         # if different parameter names are desired, get them from the samples
@@ -671,7 +673,10 @@ def copy_samples(self, other, parameters=None, parameter_names=None,
             samples = FieldArray.from_kwargs(**arrs)
             other.attrs['variable_params'] = samples.fieldnames
         logging.info("Writing samples")
-        other.write_samples(other, samples, **write_args)
+        if write_args is None:
+            write_args = {}
+        other.write_samples({p: samples[p] for p in samples.fieldnames},
+                            **write_args)
 
     def copy(self, other, ignore=None, parameters=None, parameter_names=None,
              read_args=None, write_args=None):

pycbc/inference/sampler/base_mcmc.py

@@ -454,8 +454,14 @@ def set_state_from_file(self, filename):
     def set_start_from_config(self, cp):
         """Sets the initial state of the sampler from config file
         """
-        init_prior = initial_dist_from_config(cp, self.variable_params)
-        self.set_p0(prior=init_prior)
+        if cp.has_option('sampler', 'start-file'):
+            start_file = cp.get('sampler', 'start-file')
+            logging.info("Using file %s for initial positions", start_file)
+            init_prior = None
+        else:
+            start_file = None
+            init_prior = initial_dist_from_config(cp, self.variable_params)
+        self.set_p0(samples_file=start_file, prior=init_prior)
 
     def resume_from_checkpoint(self):
         """Resume the sampler from the checkpoint file