Added missing assert

dlib/matrix/matrix_fft.h

@@ -238,6 +238,8 @@ namespace dlib
                   and then finishes with a radix-2 or -4 iteration if needed.
         !*/
         {
+            COMPILE_TIME_ASSERT((is_same_type<double,T>::value || is_same_type<float,T>::value || is_same_type<long double,T>::value ));
+
             if (data.size() == 0)
                 return;
 

dlib/matrix/matrix_fft_abstract.h

@@ -28,7 +28,7 @@ namespace dlib
     );  
     /*!
         requires
-            - data contains elements of type std::complex<>
+            - data contains elements of type std::complex<> that itself contains double, float, or long double.
             - is_power_of_two(data.nr()) == true
             - is_power_of_two(data.nc()) == true
         ensures
@@ -50,7 +50,7 @@ namespace dlib
     );  
     /*!
         requires
-            - data contains elements of type std::complex<>
+            - data contains elements of type std::complex<> that itself contains double, float, or long double.
             - is_power_of_two(data.nr()) == true
             - is_power_of_two(data.nc()) == true
         ensures
@@ -76,7 +76,7 @@ namespace dlib
     );
     /*!
         requires
-            - data contains elements of type std::complex<>
+            - data contains elements of type std::complex<> that itself contains double, float, or long double.
             - is_power_of_two(data.nr()) == true
             - is_power_of_two(data.nc()) == true
         ensures
@@ -99,7 +99,7 @@ namespace dlib
     );
     /*!
         requires
-            - data contains elements of type std::complex<>
+            - data contains elements of type std::complex<> that itself contains double, float, or long double.
             - is_power_of_two(data.nr()) == true
             - is_power_of_two(data.nc()) == true
         ensures