Document matfaust.fact.butterfly and add dir='left'|'right' argument.

wrapper/matlab/+matfaust/+fact/butterfly.m

 % experimental block start
 %==========================================================================
-%> @brief Factorizes the matrix M according to the butterfly support.
+%> @brief Factorizes the matrix M according to a butterfly support.
+%>
+%> @param 'dir', str: the direction of factorization 'right'ward or 'left'ward
+%>         (more precisely: at each stage of the factorization the most right factor or
+%>          the most left factor is split in two).
+%>
+%> @retval F the Faust which is an approximate of M according to a butterfly support.
 %==========================================================================
-function F = butterfly(M)
-	import matfaust.Faust
-	if(isreal(M))
-		core_obj = mexButterflyReal(M);
-	else
-		core_obj = mexButterflyCplx(M);
-	end
-	F = Faust(core_obj, isreal(M));
+function F = butterfly(M, varargin)
+        import matfaust.Faust
+        nargin = length(varargin);
+        dir = 'right';
+        if(nargin > 0)
+                for i=1:nargin
+                        switch(varargin{i})
+                                case 'dir'
+                                        if(nargin < i+1 || ~ any(strcmp(varargin{i+1}, {'right', 'left'})))
+                                                error('keyword argument ''dir'' must be followed by ''left'' or ''right''')
+                                        else
+                                                dir = varargin{i+1};
+                                        end
+                        end
+                end
+        end
+        if(strcmp(dir, 'right'))
+                dir = 1;
+        elseif(strcmp(dir, 'left'))
+                dir = 0;
+        end
+        if(isreal(M))
+                core_obj = mexButterflyReal(M, dir);
+        else
+                core_obj = mexButterflyCplx(M, dir);
+        end
+        F = Faust(core_obj, isreal(M));
 end
+
 % experimental block end

wrapper/matlab/src/mexButterfly.cpp.in

@@ -72,16 +72,18 @@ void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
 
 	if (nrhs < 1)
 	{
-		mexErrMsgTxt("Bad Number of inputs arguments (must be 1)");
+		mexErrMsgTxt("Bad Number of inputs arguments (must be at least 1)");
 	}
 	try
 	{
+		ButterflyFactDir dir = RIGHT;
+		if(nrhs >= 2)
+			dir = static_cast<ButterflyFactDir>(static_cast<int>(mxGetScalar(prhs[1])));
 		TransformHelper<SCALAR, Cpu>* F = nullptr;
 		Faust::MatDense<SCALAR,Cpu> matrix;
-		mxArray2FaustMat(prhs[0],matrix);
+		mxArray2FaustMat(prhs[0], matrix);
 
-		F = Faust::butterfly_hierarchical(matrix);
-		F->display();
+		F = Faust::butterfly_hierarchical(matrix, dir);
 		plhs[0] = convertPtr2Mat<Faust::TransformHelper<SCALAR, Cpu>>(F);
 	}
 	catch (const std::exception& e)