Prevent repeated psi4 correction.

bilby/gw/detector/psd.py

@@ -55,6 +55,7 @@ class PowerSpectralDensity(object):
             self.asd_array = asd_array
         self.psd_file = psd_file
         self.asd_file = asd_file
+        self.__is_psi4_psd = False
 
     def _update_cache(self, frequency_array):
         psd_array = self.power_spectral_density_interpolated(frequency_array)
@@ -229,11 +230,13 @@ class PowerSpectralDensity(object):
         return psi4_psd
 
     def convert_strain_power_spectral_density_to_psi4_power_spectral_density(self, sampling_frequency):
-        psi4_psd = self.psi4_power_spectral_density(self.psd_array, self.frequency_array, 1/sampling_frequency)
-        self.__psd_array_bkup = self.psd_array
-        self.__psd_array = psi4_psd
-        self.__asd_array = psi4_psd ** 0.5
-        self.__interpolate_power_spectral_density()
+        if not self.__is_psi4_psd:
+            psi4_psd = self.psi4_power_spectral_density(self.psd_array, self.frequency_array, 1/sampling_frequency)
+            self.__psd_array_bkup = self.psd_array
+            self.__psd_array = psi4_psd
+            self.__asd_array = psi4_psd ** 0.5
+            self.__interpolate_power_spectral_density()
+            self.__is_psi4_psd = True
 
     @property
     def psd_array(self):