Error using for-loop, keep getting "Index in position 1 is invalid. Array indices must be positive integers or logical values."

Hi everyone,

I am currently writing code that will loop through twice and call a Psat(T,A,B,C) function to calculate Psat(i) (twice for each temperature.) Here is my code:

%% Using single-temperature to plot simple P-XY diagram
%% @ T = 273.15
% Propane, Isobutane
ConstantA = [3.98292 4.3281];
ConstantB = [819.296 1132.108];
ConstantC = [-24.417 0.918];
T = 273.15; 
for i=1:2
    Psat(i) = Psat(T, ConstantA(i), ConstantB(i), ConstantC(i));
end

and the Function Psat:

function Psat = Psat(temp, a, b, c) 
Psat = 10^(a - b/(temp+c)); % Antoine's Eqn
Psat = Psat*0.133322;
end

I don't understand why I keep getting index errors. The constant matrix are vectors of size [1,2] and the numbers I'm incrementing over are whole or (+) (AKA 1-2). Even when I was attempting to de-bug, I would remove Psat(i) all together and just loop through for ConstantA(i) and still get the same indexing error?

Thank you!

Answer 1

[Star Strider]

The variable and the function have the same names.

Change the function name and it works —

%% Using single-temperature to plot simple P-XY diagram
%% @ T = 273.15
% Propane, Isobutane
ConstantA = [3.98292 4.3281];
ConstantB = [819.296 1132.108];
ConstantC = [-24.417 0.918];
T = 273.15; 
for i=1:2
    Psat(i) = Psatfcn(T, ConstantA(i), ConstantB(i), ConstantC(i));
end

Psat

Psat = 1×2

0.6515 0.2100

% and the Function Psat:
function Psat = Psatfcn(temp, a, b, c) 
Psat = 10^(a - b/(temp+c)); % Antoine's Eqn
Psat = Psat*0.133322;
end

.

[Brandon]

Wait, Thank you so much!

[Star Strider]

My pleasure!

If my Answer helped you solve your problem, please Accept it!

.