Error using semilogx Data cannot have more than 2 dimensions. Error in aaaa (line 39) semilogx(V,P); xlim([1 100]); HOW CAN I SOLVE THİS PROBLEM? PLEASE HELP ME

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Mustafa Batuhan Turaç 2022-5-25

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回答： Chetan 2023-9-15

%Plot P-V diagram of a given substance using peng-Robinson equation of states

%Substance properties are defined by the van der Waals constants and

%the critical properties.

clc; clear; close all;

Tc = 765.62; % R

Pc = 550.60; % psi

Vc = 0.0703; % ft3/lbmole

R = 10.732; % psi ft3/(lbmole-R)

% peng-Robinson Equation of State Constants

% for n-Butane

a = 54566;

b = 1.161;

V = linspace(b*1.2,40*Vc,100); % vector of volume

% temperature in F

T = [60 180 230 270 300 306];

T = T + 460; % temperature in R

H = [1.2501 1.1184 1.0692 1.0318 1.0049 0.9996];

% peng-Robinson Equation

fPRWEOSp = @(Tx,Vx,Hx)(R*Tx./(Vx-b)-a*Hx./(Vx.^2 + 2*Vx*b-b^2));

P = zeros(numel(T), numel(V), numel(H));

for j=1:numel(H)

for i= 1:numel(T)

Tx = T(i);

Hx = H(j);

P(i,:,j) = fPRWEOSp(Tx,V,Hx);

end

% plot(V,P); xlim([0 100]);

semilogx(V,P); xlim([1 100]);

ylim([0 800]);

xlabel('Volume, ft^3');

ylabel('Pressure, psi');

Error using semilogx

Data cannot have more than 2 dimensions.

Error in aaaa (line 39)

semilogx(V,P); xlim([1 100]);

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Answer 1

Chetan 2023-9-15

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Hello Mustafa,

It appears that you are encountering an issue while plotting data with different temperatures and enthalpy using the "simlogx" function.

The error message "Data cannot have more than 2 dimensions" occurs because the "semilogx" function in MATLAB expects the input data to be two-dimensional.

In your code, the variable P has three dimensions

(numel(T) x numel(V) x numel(H)),

which causes the error. To resolve this issue and plot the P-V diagram for each temperature, you need to split the data and obtain a two-dimensional format.

This can be done by either squeezing the array or using a for loop for indexing.

To understand the working of the "squeeze" function and the "semilogx" function, I recommend reading the following articles: