Error in Line 13 of mapper.m file

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function [modulated_symbols,Mod] = mapper(b,N)
% If N is given, it generates a block of N random 2^b-PSK/QAM modulated symbols.
% Otherwise, it generates a block of 2^b-PSK/QAM modulated symbols for [0:2^b-1].

% MIMO-OFDM Wireless Communications with MATLAB¢ç Yong Soo Cho, Jaekwon Kim, Won Young Yang and Chung G. Kang
% 2010 John Wiley & Sons (Asia) Pte Ltd

% http://www.wiley.com//legacy/wileychi/cho/

M=2^b; % Modulation order or Alphabet (Symbol) size
if b==1, Mod='BPSK'; A=1; mod_object=modem.pskmod('M',M);
elseif b==2, Mod='QPSK'; A=1;
mod_object=modem.pskmod('M',M,'PhaseOffset',pi/4);
else Mod=[num2str(2^b) 'QAM']; Es=1; A=sqrt(3/2/(M-1)Es);
mod_object=modem.qammod('M',M,'SymbolOrder','gray');
end
if nargin==2 % generates a block of N random 2^b-PSK/QAM modulated symbols
modulated_symbols = Amodulate(mod_object,randint(1,N,M));
else
modulated_symbols = A*modulate(mod_object,[0:M-1]);
end