why am i getting this errror "Index exceeds matrix dimensions"

% Following is a function which performs Dew T calculation for

% Water-Ethanol system using Raoults LAw

% Similar Method can be followed for Modified Raoults Law and Dew P, Bubble

% P, Bubble T calculations

function F=system(x,a)

% Specie 1 is water and specie 2 is ethanol

%x(1) is x1

%x(2) is x2

%x(3) is y1

%x(4) is y2

%x(5) is T

%x(6) is P

%x(7) is P1sat

%x(8) is P2sat

F(1)= exp(x(7))==(16.3872-((3885.70)/(x(5)+230.170)));% Water Antoine Equation

F(2)= exp(x(8))==(16.8958-((3795.17)/(x(5)+230.918))); % Ethanol Antoine Equation

F(3)= x(1)*x(7)- x(3)*x(6); % Raoiults Law for water

F(4)= x(2)*x(8)- x(4)*x(6); % Raoiults Law for Ethanol

F(5)= x(1)+x(2)-1; % fractions reation to each other

F(6)=x(3)+ x(4)-1; % fractions reation to each other

F(7)=x(6)-(200); % input of Pressure

F(8)=x(3)-a; % input of y1

% number of variables are now equal to number of equations

a=0:0.1:1;

for ct = 1:numel(a)

x0 = [0.5,0.5,0.5,0.5,273,100,200,200];

options = optimoptions('fsolve','Display','iter');

x(ct,:)= fsolve(@(x)system(x,a(ct)),x0)

end

for i=1:1:10

xvalue(1,i)=x(i,4);

yvalue(1,i)=x(i,2);

end

plot(xvalue,yvalue)

Error:

Index exceeds matrix dimensions. Error in Sample13 (line 16) F(1)= exp(x(7))==(16.3872-((3885.70)/(x(5)+230.170)));% Water Antoine Equation

Answer 1

[Walter Roberson]

Move the function to the end of the file.

Also,

F(1)= exp(x(7))==(16.3872-((3885.70)/(x(5)+230.170)));% Water Antoine Equation
F(2)= exp(x(8))==(16.8958-((3795.17)/(x(5)+230.918))); % Ethanol Antoine Equation

Rewrite those as left side minus right side. MATLAB needs the sign information to know which direction to steer the variables.

[Ahmed Saleem]

Thnx man