Interpolating between calling specific elements of the table

Hello,

I have created this table of thermodynamic properties, however, I would like to be able to obtain a linearly interpolated value whenever the property I insert on my function is in between two values as listed on the table. I have tried different things such as 'if' function, but i cannot even start getting the progam to run with those.

The way the function works is I insert a pressure value for example instead of P, and a desired column from which i would like to obtain the property: i.e. R134a(80,'temp').

Any help would be greatly appreciated. Thanks in advance!

Below is the function:

function out=R134a(P,a)

M=[60 -36.9 0.0007098 0.3112 3.8 209.1 3.9 223.9 227.8 0.0164 0.9481 0.9645; 80 -31.1 0.0007185 0.2376 11.2 212.5 11.2 220.2 231.5 0.0472 0.9100 0.9572];

T=array2table(M,'variablenames',{'pres', 'temp','v_f','v_g', 'u_f', 'u_g', 'h_f', 'h_fg', 'h_g', 's_f', 's_fg', 's_g'}); [I,J]=find(M==P); T(I,a)

end

[Peter Perkins]

Kosta, I think you're going to have to give a short example of exactly what you need to do.

Answer 1

[Ahmet Cecen]

Had something like this already, here it is:

 function out=R134a(P,a)

    % Your Table
    M=[60  -36.9  0.0007098  0.3112  3.8  209.1  3.9  223.9  227.8  0.0164  0.9481  0.9645; ...
       80  -31.1  0.0007185  0.2376 11.2  212.5  11.2  220.2  231.5  0.0472  0.9100  0.9572];

    T=array2table(M,'variablenames',{'pres', 'temp','v_f','v_g', 'u_f', 'u_g', 'h_f', 'h_fg', 'h_g', 's_f', 's_fg', 's_g'}); 

    % Find the location of 2 nearest Pressure Values in the Table - This can accomodate
    % larger tables.
    lowerPind = max(find( M(:,1) <= P ));
    higherPind = min(find( M(:,1) >= P ));

    % Find the interpolated value
    if higherPind ~= lowerPind
        out = T{lowerPind,a} + (P-M(lowerPind,1))*(T{higherPind,a} - T{lowerPind,a}) /...
                                                  (M(higherPind,1) - M(lowerPind,1));
    else
        out = T{lowerPind,a};
    end

 end

[Kosta]

Thanks! I actually managed to use the interp1 function, it seems quite useful.