xlsread to an array by user input with interpolation

Problem getting the user inputs for Pressure (P1 & P2) to extract an array. The left column of the spreadsheet imported will be the Pressure, column 2 will be Temperature, 3 enthalpy, 4 entropy.

What I am trying to do is take P1 and P2 from the user input and pull the respective row of P1 and P2. If they do not match the exact numbers in the spreadsheet that I have (there is 10-40 numbers between each pressure value) then the code should execute a linear interpolation routine to find the exact enthalpy and entropy.

Answer 1

[Guillaume]

Use interp1 to get your temperature, enthalpy and entropy for both P1 and P2 all at once. The simplest way is to keep all these values together in a matrix:

   sat_interpolated = interp1(sat_numeric(:, 1), sat_numeric(:, 2:end), [P1, P2]);
   %column 1, 2, 3 of sat_interpolated are T, H, S respectively. row 1 is P1, row 2 is P2

As an aside:

P1 = input(SomePrompt)
while P1 < 0 || P1 > 1600
   P1 = input(ExactSamePromptThatYouHadToRetype)
end

could be written more simply as

P1 = -Inf
while P1 < 0 || P1 > 1600
   P1 = input(PromptThatYouOnlyHaveToWriteOnce)
end

Same for P2.

[Jared Smothers]

Thank you for your assistance... I should elaborate a bit more. P1 & P2 are two pressures in two different states. P1 comes from a Tab 1 (Saturated_R134a) and P2 comes from Tab 2 (Superheated_R134a) of my spreadsheet (Thermodynamics_R134a_tables.xls).

I suppose it would need to be something like the statement above but inside of an "if" statement?

If the user defined P1 doesnt match one of the numbers in column 1 then calculate a regression in the middle of the two closest figures.

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[Jared Smothers]