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function [isOk, status] = istrellis(S)
// This function checks if the given input is of trellis structure
//
// Calling Sequence
// [ISOK, STATUS] = ISTRELLIS(S)
//
// Description
// [ISOK, STATUS] = ISTRELLIS(S) returns [T,''] if the given input is valid trellis structure. Otherwise ISOK is F and STATUS
// indicates the reason for invalidity
//
// Fields in trellis structure are
// numInputSymbols, (number of input symbols)
// numOutputSymbols, (number of output symbols)
// numStates, (number of states)
// nextStates, (next state matrix)
// outputs, (output matrix)
//
// Properties of the fields are as follows
// numInputSymbols and numOutputSymbols should be a power of 2 (as data is represented in bits).
// The 'nextStates' and 'outputs' fields are matrices of size 'numStates' x 'numInputSymbols' .
// Each element in the 'nextStates' matrix and 'output' matrix is an integer value between zero and (numStates-1).
// The (r,c) element of the 'nextStates' matrix and 'output' matrix,denotes the next state and output respectively when
// the starting state is (r-1) and the input bits have decimal representation (c-1).
//
// To convert to decimal value, use the first input bit as the most significant bit (MSB).
//
// Examples
// Valid trellis structure
// trellis.numInputSymbols = 4;
// trellis.numOutputSymbols = 4;
// trellis.numStates = 3;
// trellis.nextStates = [0 1 2 1;0 1 2 1; 0 1 2 1];
// trellis.outputs = [0 0 1 1;1 1 2 1; 1 0 1 1];
// [isok,status] = istrellis(trellis)
//
// Inavlid trellis structure
// trellis.numInputSymbols = 3;
// trellis.numOutputSymbols = 3;
// trellis.numStates = 3;
// trellis.nextStates = [0 1 2 ;0 1 2 ; 0 1 2 ];
// trellis.outputs = [0 0 1 ;1 1 2 ; 1 0 1 ];
// [isok,status] = istrellis(trellis)
//
// Authors
// Pola Lakshmi Priyanka, IIT Bombay
//*************************************************************************************************************************************//
// Check arguments
[out_a,inp_a]=argn(0)
if (inp_a~=1 | out_a>2) then
error('comm:istrellis:Invalid number of arguments')
end
status = '';
// Check if input is a structure
isOk = isstruct(S);
if ~isOk then
status = string(('comm:trellis:Input is not a structure'));
return;
end
// Check for valid field names
names = fieldnames(S);
numf = size(names, 1);
actual = {'numInputSymbols';'numOutputSymbols';'numStates';'nextStates';'outputs'}
isOk = (numf == 5) & isequal(gsort(names),gsort(actual));
if ~isOk then
status = string(('comm:trellis:Structure is not of trellis type'));
return;
end
// Check for number of Input Symbols.
numInputSymbols = S.numInputSymbols;
isOk = isequal(length(numInputSymbols), 1);
if ~isOk then
status = string(('comm:trellis:Number of input symbols is not scalar'));
return;
end
power = log2(numInputSymbols);
isOk = isequal(power, double(int32(power)));
if ~isOk then
status = string(('comm:trellis:Number of input symbols is not power of 2'));
return;
end
// Check for number of Output Symbols.
numOutputSymbols = S.numOutputSymbols;
isOk = isequal(length(numOutputSymbols), 1);
if ~isOk then
status = string(('comm:trellis:Number of output symbols is not scalar'));
return;
end
power = log2(numOutputSymbols);
isOk = isequal(power, double(int32(power)));
if ~isOk then
status = string(('comm:trellis:Number of input symbols is not power of 2'));
return;
end
//Check Number of states
isOk = isequal(length(S.numStates), 1) & ...
isequal(S.numStates, double(int32(S.numStates)));
if isOk then
isOk = S.numStates > 0;
end
if ~isOk then
status = string(('comm:trellis:Number of states is not scalar positive integer'));
return;
end
// Check nextStates
nextStates = S.nextStates;
numStates = S.numStates;
// Check size of nextStates
s = size(nextStates);
isOk = ((length(s) == 2) & (s(1) == numStates) & (s(2) == numInputSymbols) & isequal(double(uint32(nextStates)), nextStates));
if ~isOk then
status = string(('comm:trellis:Next states field matrix size is incorrect'));
return;
end
//Check values of nextState
isOk = isempty(find(nextStates >= numStates));
if ~isOk then
status = string(('comm:trellis: Elements in next state must be in between 0 to numStates - 1'));
return;
end
// Check outputs
outputs = S.outputs;
// check size of outputs
s = size(outputs);
isOk = ((length(s) == 2) & (s(1) == numStates) & (s(2)== numInputSymbols) );
if ~isOk then
status = string(('comm:trellis:Outputs field matrix size is incorrect'));
return;
end
//Check values of output
decOutputs = oct2dec(string(outputs));
isOk = isempty(find(decOutputs >= numOutputSymbols));
if ~isOk then
status = string(('comm:trellis: Elements in output must be in between 0 to numStates - 1 '));
return;
end
endfunction
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