MATLAB: Function file not behaving

codeerrorfunctionMATLAB

When trying to run this function, every time it comes up with an error which I'm not sure where it is.
I'm calling it using the code, and getting the error:
[BPE] = BPE(T_f, X_f)
And I'm getting these errors:
??? Attempted to access BPE(69.81,42); index must be a positive integer or logical.
?? Index exceeds matrix dimensions
??? Attempted to access BPE(69,42); index out of bounds because numel(BPE)=1.
T_f = 69.81 and X_f = 42
This is my function file:
function [BPE] = BPE(T, X)
% A function to calculate The Boiling point elevation in degrees Celcius
A = (8.325e-2 + 1.883e-4 * T + 4.02e-6 * T^2);
B = (-7.625e-4 + 9.02e-5 * T - 5.2e-7 * T^2);
C = (1.522e-4 - 3e-6 * T - 3e-8 * T^2);
BPE = 100 * A*X + B*X^2 + C*X^3;
end
Any thoughts as to why this is failing?
Thanks in advance.

Best Answer

Don't name your output variable the same as the function. Because after you output BPE once, then it's a variable in the workspace and you subsequently try to access a non-integer element of a variable (a scalar in this case).
Change the name of the output argument in your function.
function [BP] = BPE(T, X)
% A function to calculate The Boiling point elevation in degrees Celcius
A = (8.325e-2 + 1.883e-4 * T + 4.02e-6 * T^2);
B = (-7.625e-4 + 9.02e-5 * T - 5.2e-7 * T^2);
C = (1.522e-4 - 3e-6 * T - 3e-8 * T^2);
BP = 100 * A*X + B*X^2 + C*X^3;
end
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