Error converting from sym to double: Unable to convert expression into double array

Hi,

I am having a problem with the syms function in matlab and I was wondering if anyone could help. The help would be greatly appreciated.

The code is to caclulate the bubblepoint of a mixture which contains n components.

The beginning of the code can be seen below. The last line is where the error :Error converting from sym to double: Unable to convert expression into double array

occurs.

CODE:

P_total = input('Please enter the total pressure in mm Hg: \n');

n = input('Please enter the number of components:\n');

x = zeros(1, n); % Liquid phase mole fractions

y = zeros(1, n); % Vapour phase mole fractions

load Antoine_coefficients.txt % reading in the file which contains the Antoine Coefficients of the components

fprintf(' 1 = Acetaldehyde\n 2 = Acetic Acid \n 3 = Acetone \n 4 = Acetylene \n 5 = Ammonia\n 6 = Argon\n 7 = Benzene \n')

for ite = 1: n

fprintf('Please enter the corresponding number for the component %i in the feed stream: \n', i);

comp(i) = input(' ');

data1 = Antoine_coefficients(comp(i),:);

a(i) = data1(1);

b(i) = data1(2);

c(i) = data1(3);

end

for i = 1:1:n

fprintf('Please input the liquid phase mole fraction of component %i: \n', i);

x(1, i) = input(' ');

end

% bubble point temp. calc

syms T [1:n]

for i = 1:1:n

% y1 = x1 * Psat/Ptotal

y(i) = x(i).*(10.^Antoine(a(i), b(i), c(i), T)./P_total); % Antoine is the user defined function which calculates Psat

end

I would really appreciate any help.

Thank in advance!

Answer 1

[Star Strider]

Try this to create ‘T’ as a vector:

n = 5                                   % Define ‘n’
syms T 
T = sym('T', [1 n])

producing:

T =
[T1, T2, T3, T4, T5]

Then address it as you would any other vector:

y3 = T(3) 

produces:

y3 =
T3

.

[Kate Kirwan]

Hi thanks for your reply! I really appreciate the response!

I have tried what you have recommended but unfortunately I get the error : Using input and output arguments simultaneously is not supported.

Do have any idea on how to ensure that this error does not occur?

Thanks in advance!

[Star Strider]

I have no idea howcode such as mine could have thrown that error. My code ran without error and produced the result I posted.