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+function result = iscatastrophic(trellis)
+
+//   This function  determines if a convolutional code is catastrophic or not
+
+//   Calling Sequence
+//   RESULT = ISCATASTROPHIC(TRELLIS)
+
+//   Description
+//   RESULT = ISCATASTROPHIC(TRELLIS) returns 1 if the specified 
+//   trellis corresponds to a catastrophic convolutional code, else 0.
+
+//   Examples 
+//   eg_1.numInputSymbols = 4;
+//   eg_1.numOutputSymbols = 4;
+//   eg_1.numStates = 3;
+//   eg_1.nextStates = [0 1 2 1;0 1 2 1; 0 1 2 1];
+//   eg_1.outputs = [0 0 1 1;1 1 2 1; 1 0 1 1];
+//   res_t_eg_1=istrellis(eg_1)
+//   res_c_eg_1=iscatastrophic(eg_1)
+//   if (res_c_eg_1) then
+//       disp('Example 1 is catastrophic')
+//   else
+//       disp('Example 1 is not catastrophic')
+//   end
+
+//   eg_2.numInputSymbols = 2;
+//   eg_2.numOutputSymbols = 4;
+//   eg_2.numStates = 2;
+//   eg_2.nextStates = [0 0; 1 1 ]
+//   eg_2.outputs = [0 0; 1 1];
+//   res_t_eg_2=istrellis(eg_2)
+//   res_c_eg_2=iscatastrophic(eg_2)
+//   if (res_c_eg_2) then
+//       disp('Example 2 is catastrophic')
+//   else
+//       disp('Example 2 is not catastrophic')
+//   end 
+
+
+//   See also
+//   istrellis
+
+//   Authors
+//   Pola Lakshmi Priyanka, IIT Bombay//
+
+//*************************************************************************************************************************************//
+
+// Check number of input arguments
+[out_a,inp_a]=argn(0)
+
+if inp_a~=1 then
+    error('comm:iscatastrophic: Invalid number of input arguments')
+end
+
+
+if out_a>1 then
+    error('comm:iscatastrophic: Invalid number of output arguments')
+end
+
+// Check if the input is a valid trellis
+if ~istrellis(trellis),
+    error('comm:iscatastrophic:Input should be a valid trellis structure.');  
+end
+
+result = 0;
+
+// Find indices of zeros in trellis structure
+[r_idx,c_idx] = find(trellis.outputs==0);
+
+//Find Connectivity matrix and check if it is catastrophic
+A = zeros(trellis.numStates,trellis.numStates);
+for k = 2:length(r_idx)
+    A(r_idx(k),trellis.nextStates(r_idx(k),c_idx(k))+1)=1;
+end
+
+
+test = A;
+for i = 1:trellis.numStates
+    for j = 1:trellis.numStates
+        if test(j,j)==1
+            result = 1
+        end
+    end
+    if result==1
+        break
+    else
+        test = test*A;
+    end
+end
+
+endfunction