function y=Phap(x,params)
% Anh - short term design stress - strain curve for normal weight concrete.
% Anh(X,PARAMS) return a matrix which is the Anh at X.
% BUI DUC CHINH,10 - 5 -2000.
% Ver 1.03.
if nargin ~=2,
   error('Three arguments are required by Anh.');
elseif length(params)<4 
   error('Anh needs at least 4 parameters.');
end
a=params(1);
b=params(2);
c=params(3);
d=params(4);
y=ones(size(x))*d;
index1=find(x<=a);
if ~isempty(index1),
   y(index1)=250*d*x(index1).*(4-x(index1)*1000);
end