Having trouble with interp2 within a for loop

Hello, I'm having a little issue with my for loop using interp2:

%For enthalpy given the temperature and pressure

p1 = 20:0.03:200;

t1 = 5:1:500;

for i = 1:length(p1)

      for j = 1:length(t1)

          rho(i,j) = interp2(p1,t1,rho_ph)

      end

end

%For density given the pressure and enthalpy

p2 = 500:1:1100;

t2 = 200;

for k = 1:length(p2)

      for l = 1:length(t1)

          h_pt(k,l) = interp2(p2,t2,h_pt)

      end

end

This is the error:

Error using griddedInterpolant
Interpolation requires at least two sample points in each dimension.

Error in interp2/makegriddedinterp (line 214)
            F = griddedInterpolant(varargin{:});

Error in interp2 (line 111)
    F = makegriddedinterp({X,Y},V,method,extrap);

I'm not really understanding what is being asked.

Answer 1

[Walter Roberson]

You have

            rho(i,j) = interp2(p1,t1,rho_ph)

p1 is a vector. t1 is a vector. rho_ph we do not know the size of.

The two allowable ways to call interp2 are:

   interp2(DataGrid, Row_query_points, Column_query_points)

and

interp2(X_information, Y_information, DataGrid, X_query_points, Y_query_points)

In the first of those two syntaxes, the one you used, the first parameter, the DataGrid, must be at least 2 x 2, but you are passing in a vector for the first part.

In the second of those two syntaxes, it is permitted for X_information and Y_information to be vectors, but you need to specify the places that you want the queries to be at.