function value = bez_val ( n, x, a, b, y )
%*****************************************************************************80
%
%% BEZ_VAL evaluates a Bezier function at a point.
%
% Discussion:
%
% The Bezier function has the form:
%
% BEZ(X) = Sum ( 0 <= I <= N ) Y(I) * BERN(N,I)( (X-A)/(B-A) )
%
% BERN(N,I)(X) is the I-th Bernstein polynomial of order N
% defined on the interval [0,1],
%
% Y(0:N) is a set of coefficients,
%
% and if, for I = 0 to N, we define the N+1 points
%
% X(I) = ( (N-I)*A + I*B) / N,
%
% equally spaced in [A,B], the pairs ( X(I), Y(I) ) can be regarded as
% "control points".
%
% Licensing:
%
% This code is distributed under the GNU LGPL license.
%
% Modified:
%
% 23 February 2004
%
% Author:
%
% John Burkardt
%
% Reference:
%
% Kahaner, Moler, and Nash,
% Numerical Methods and Software,
% Prentice Hall, 1989.
%
% Parameters:
%
% Input, integer N, the order of the Bezier function, which
% must be at least 0.
%
% Input, real X, the point at which the Bezier function should
% be evaluated. The best results are obtained within the interval
% [A,B] but X may be anywhere.
%
% Input, real A, B, the interval over which the Bezier function
% has been defined. This is the interval in which the control
% points have been set up. Note BEZ(A) = Y(0) and BEZ(B) = Y(N),
% although BEZ will not, in general pass through the other
% control points. A and B must not be equal.
%
% Input, real Y(0:N), a set of data defining the Y coordinates
% of the control points.
%
% Output, real VALUE, the value of the Bezier function at X.
%
if ( b - a == 0.0E+00 )
fprintf ( 1, '\n' );
fprintf ( 1, 'BEZ_VAL - Fatal error!\n' );
fprintf ( 1, ' Null interval, A = B = %f\n', a );
error ( 'BEZ_VAL - Fatal error!' );
end
%
% X01 lies in [0,1], in the same relative position as X in [A,B].
%
x01 = ( x - a ) / ( b - a );
bval = bp01 ( n, x01 );
value = y(1:n+1) * bval(1:n+1)';
return
end