function rx = vecrotx(angle)
% 
% VECROTX: Transformation matrix for a rotation around the x axis. 
% 
% Calling Sequence:
% 
%   rx = vecrotx(angle);
% 
% INPUT:
% 
%   angle		: rotation angle defined in radians
%
% OUTPUT:
% 
%   rx		: (4x4) Transformation matrix.
% 
% 
% Description:
% 
%   Return the (4x4) Transformation matrix for a rotation about the x axis
%   by the defined angle.
% 
%   The matrix is:
% 
%         [ 1         0            0          0]
%         [ 0     cos(angle)  -sin(angle)     0]
%         [ 0     sin(angle)   cos(angle)     0]
%         [ 0         0            0          1]
% 
% Examples:
% 
%    Rotate the NURBS line (0.0 0.0 0.0) - (3.0 3.0 3.0) by 45 degrees
%    around the x-axis
% 
%    line = nrbline([0.0 0.0 0.0],[3.0 3.0 3.0]);
%    trans = vecrotx(%pi/4);
%    rline = nrbtform(line, trans);
% 
% See also:
% 
%    nrbtform
%
%    Copyright (C) 2000 Mark Spink
%
%    This program is free software: you can redistribute it and/or modify
%    it under the terms of the GNU General Public License as published by
%    the Free Software Foundation, either version 3 of the License, or
%    (at your option) any later version.

%    This program is distributed in the hope that it will be useful,
%    but WITHOUT ANY WARRANTY; without even the implied warranty of
%    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%    GNU General Public License for more details.
%
%    You should have received a copy of the GNU General Public License
%    along with this program.  If not, see <http://www.gnu.org/licenses/>.

sn = sin(angle);
cn = cos(angle);
rx = [1 0 0 0; 0 cn -sn 0; 0 sn cn 0; 0 0 0 1];

end