function steam
% steam  Sample interpolation in a steam table:  set up and
%        solve 4 equations in 4 unknowns

p = [1 1 2 2]';
T = [250 500 250 500]';
h = [2942.6 3478.5 2902.5 3467.6]';

A = [ ones(4,1)  p  T  p.*T]
c = A\h;

fprintf('\nSolution is:  c = \n');
fprintf('\t%18.5e\n',c); 

Ttest = [ 250  400 ]';
ptest = [1  1.75]';

htest = c(1) + c(2)*ptest(1) + c(3)*Ttest(1) + c(4)*ptest(1)*Ttest(1)


htest - h(1)