Add analytical formula in DCT/DST doc.

wrapper/matlab/+matfaust/dct.m

 %=========================================
 %> @brief Returns the Direct Cosine Transform (Type II) Faust of order n.
 %>
+%> The analytical formula of DCT II used here is:
+%> \f$2 \sum_{n=0}^{N-1} x_n cos \left( {\pi k (2n + 1)} \over {2N} \right)\f$
+%>
 %> @param n: the order of the DCT (it must be a power of two).
 %> @param 'dev', str: 'gpu' or 'cpu' to create the Faust on CPU or GPU ('cpu' is the default).
 %>

wrapper/matlab/+matfaust/dst.m

 %=========================================
 %> @brief Returns the Direct Sine Transform (Type II) Faust of order n.
 %>
-%> @param n: the order of the DCT (it must be a power of two).
+%> The analytical formula of DST II used here is:
+%> \f$2 \sum_{n=0}^{N-1} x_n sin \left( {\pi (k+1) (2n + 1)} \over {2N} \right)\f$
+%>
+%> @param n: the order of the DST (it must be a power of two).
 %> @param 'dev', str: 'gpu' or 'cpu' to create the Faust on CPU or GPU ('cpu' is the default).
 %>
 %> @b Example

wrapper/python/pyfaust.py

@@ -3302,6 +3302,10 @@ def dft(n, normed=True, dev='cpu'):
 def dct(n, dev='cpu'):
     """Returns the Direct Cosine Transform (Type II) Faust of order n.
 
+    The analytical formula of DCT II used here is:
+        \f$2 \sum_{n=0}^{N-1} x_n cos \left( {\pi k (2n + 1)} \over {2N} \right)\f$
+
+
     Args:
         n: the order of the DCT (must be a power of two).
         dev: the device on which the Faust is created.
@@ -3398,6 +3402,9 @@ def dst(n, dev='cpu'):
     """
     Returns the Direct Sine Transform (Type II) Faust of order n.
 
+    The analytical formula of DST II used here is:
+        \f$2 \sum_{n=0}^{N-1} x_n sin \left( {\pi (k+1) (2n + 1)} \over {2N} \right)\f$
+
     Args:
         n: the order of the DST (must be a power of two).
         dev: the device on which the Faust is created.