spline interpolation between three values

I have pressure ,tempreature and density data and I want to make spline interpolation that fits all

so I have P=[100 200 300];

T=[100 150 400];

density=[0.4,0.7.0.8]

so i need to get spline function for p,t and density I found onle splin function for two parameter only

Answer 1

[Chunru]

P=[100 200 300];
T=[100 150  400];
density=[0.4,0.7,0.8];

Pq =100:300;
Tq = spline(P, T, Pq);
dq = spline(P, density, Pq);

subplot(121); plot(P, T, 'o', Pq, Tq, 'b-');
subplot(122); plot(P, density, 'o', Pq, dq, 'b-');