function  A = m_sin(b,X)
% A = m_sin(b,X)
%
% The function returns the exponent values of X(:). The formula is:
% $$ A_j = sin (c_j x + s_j) $$
% The vector b contains n/2 groups of coefficients: c(j) = b(2j-1) is a
% coefficient before x and s(j) = b(2j) is a phase shift.
%
% Notation:
% X [m x 1] is an input column vector,
% b [1 x 2n] is a parameters vector, where n is a number of items in the
% non-linear mapping.
% A [m x n] is an output matrix of the non-linear  mappings, where each
% column corresponds to an item of the further linear combination. 
%
% Example
% y = m_sin([20,0],linspace(0,1,10)) 
%
c = b(1:2:end-1); % 2 parameters; even parameters are coeffs
s = b(2:2:end);   % 2 parameters; odd parameters are phase shifts
n = length(b)/2; % n components 
m = length(X);
A = repmat(X(:),[1 n]) * diag(c) + repmat(s,[m 1]); 
A = sin( A );    
return