Arrays have incompatible sizes for this operation

clc;
clear;
%This function is will determine the rate of heat loss
%you will experience through one of our select pipes and
%piping insulation
pipe=questdlg('Choose your pipe material','Pipe Material','copper','stainless steel','aluminum', 'aluminum');
insulation=questdlg('Choose your type of insulation','insulation','glass wool','rigid foam','no insulation','no insulation');
%Below are the inputs for the pipe dimensions
inner=input('Enter pipe inner diameter in mm:');
thickness=input('Enter pipe thickness in mm:');
ithickness=input('Enter insulation thickness in mm:');
L=input('Enter pipe length in m:');
%The below section handles temperatures. All temps calculated within
%fuction are calculated using celcius.
t2=input('Enter approximate room temperature(Temperature outside of pipe and insulation):');
fprintf('This next input will be related to steam temperature. Enter either a single value or \nrange of values.\n')
fprintf('If entering a range of values, enter as a vector with incrementally equal values \nranging from 200 to 500 degrees celcius or 392 to 932 degrees Farenheit.\n')
pause(3)
t1=input('Input temperature of steam:');
unit=questdlg('Are the temperatures you entered in celcius or farenheit?','Temp Unit','F','C','C');
if unit=='F'
    T1=(t1-32)*5/9;
    T2=(t2-32)*5/9;
else unit=='C'
    T1=t1;
    T2=t2;
end
if T1 > 500 | T1 < 200
    disp('Please enter a temperature between 200C and 500C')
    pause(3)
    tempfunction()
end
%The section below handles the coefficients of heat transfer for the
%equation to solve.
if pipe=='copper'
    if T1 >= 200 & T1 <= 350 
        k = 386;
    else T1 >= 351 & T1 <= 500
        k = 379;
    end
    
elseif pipe=='stainless steel'
    k=50        %W/m K
else pipe=='aluminum'
    if T1>=200 & T1<=350
        k = 159;
    elseif T1>=351 & T1<=450
        k = 172;
    else T1>450
        k=185;
    end
end
if insulation=='glass wool'
    k2=.05;
elseif insulation=='rigid foam'
    k2=.02;
else insulation=='no insulation'
    k2=0;
end
%heat transfer coefficient inside the pipe = 60 W/m^2*K(From 
h1=60;
%heat transfer coefficient outside the pipe = 18 W/m^2*K
h2=18;
%To get radii
r1=inner/2;
r2=(inner/2)+thickness;
r3=(inner/2)+thickness+ithickness;
%Now we will calculate the surface areas exposed to convection
A1=2*pi*r1*L;
A2=2*pi*r2*L;
%Now we will calculate the individual thermakl resistance network
Rconv1=1/(h1*A1);
R1=log(r2/r1)/(2*pi*k*L);
R2=log(r3/r2)/(2*pi*k2*L);
Rconv2=1/(h2*A2);
fprintf('Here are the values for your thermal resistance network')
pause(2);
fprintf('Rconv1= %6.3f C/W\n',Rconv1);
pause(2);
fprintf('R1= %6.3f C/W\n', R1);
pause(2);
fprintf('R2= %6.3f C/W\n',R2);
pause(2);
fprintf('Rconv2= %6.3f C/W\n',Rconv2);
%Now we will add up the total thermal resistance
R=Rconv1+R1+R2+Rconv2;
pause(5);
fprintf('Your total thermal resistance is %6.3f C/W.\n',R);
%Calculate the rate of heatloss
Qdot=(T1-T2)/R;  %W
pause(3);
fprintf('Your rate of heat loss through our pipe, as spec''d, will\nbe %6.3f W per meter of pipe.\n',Qdot);
pause(3);
Qtotal=Qdot*L;
fprintf('Total heat loss through the pipe will be %6.3f W.\n', Qtotal);
Tdrop=Qdot*R1;
fprintf('The drop in temperature along the pipe will be %6.3f degrees C.\n',Tdrop);
figure(1)
plot(Qdot,T1,'bs:');
title('Qdot verses T1');
xlabel('Qdot');
ylabel('T1');

On my code, when we select anything other than copper for pipe, it gives me an error message,

Arrays have incompatible sizes for this operation.

Error in testfunction (line 55)

if pipe=='copper'

Why is it doing this?

P.S. This was a function but I turned it into a script to try and troubleshoot.

Answer 1

[Torsten]

You should look up characters and if-statements in the documentation.

clc;
clear;
%This function is will determine the rate of heat loss
%you will experience through one of our select pipes and
%piping insulation
pipe="stainless steel";%questdlg('Choose your pipe material','Pipe Material','copper','stainless steel','aluminum', 'aluminum');
insulation="glass wool";%questdlg('Choose your type of insulation','insulation','glass wool','rigid foam','no insulation','no insulation');
%Below are the inputs for the pipe dimensions
inner=100;%input('Enter pipe inner diameter in mm:');
thickness=5;%input('Enter pipe thickness in mm:');
ithickness=10;%input('Enter insulation thickness in mm:');
L=1;%input('Enter pipe length in m:');
%The below section handles temperatures. All temps calculated within
%fuction are calculated using celcius.
t2=25;%input('Enter approximate room temperature(Temperature outside of pipe and insulation):');
fprintf('This next input will be related to steam temperature. Enter either a single value or \nrange of values.\n')

This next input will be related to steam temperature. Enter either a single value or 
range of values.

fprintf('If entering a range of values, enter as a vector with incrementally equal values \nranging from 200 to 500 degrees celcius or 392 to 932 degrees Farenheit.\n')

If entering a range of values, enter as a vector with incrementally equal values 
ranging from 200 to 500 degrees celcius or 392 to 932 degrees Farenheit.

%pause(3)
t1=450;%input('Input temperature of steam:');
unit="C";%questdlg('Are the temperatures you entered in celcius or farenheit?','Temp Unit','F','C','C');
if unit=="F"
    T1=(t1-32)*5/9;
    T2=(t2-32)*5/9;
elseif unit=="C"
    T1=t1;
    T2=t2;
end
if T1 > 500 | T1 < 200
    disp('Please enter a temperature between 200C and 500C')
    %pause(3)
    %tempfunction()
end
%The section below handles the coefficients of heat transfer for the
%equation to solve.
if pipe=="copper"
    if T1 >= 200 & T1 <= 350 
        k = 386;
    elseif T1 >= 351 & T1 <= 500
        k = 379;
    end 
elseif pipe=="stainless steel"
    k=50 ;       %W/m K
elseif pipe=="aluminum"
    if T1>=200 & T1<=350
        k = 159;
    elseif T1>=351 & T1<=450
        k = 172;
    elseif T1>450
        k=185;
    end
end
if insulation=="glass wool"
    k2=.05;
elseif insulation=="rigid foam"
    k2=.02;
elseif insulation=="no insulation"
    k2=0;
end
%heat transfer coefficient inside the pipe = 60 W/m^2*K(From 
h1=60;
%heat transfer coefficient outside the pipe = 18 W/m^2*K
h2=18;
%To get radii
r1=inner/2;
r2=(inner/2)+thickness;
r3=(inner/2)+thickness+ithickness;
%Now we will calculate the surface areas exposed to convection
A1=2*pi*r1*L;
A2=2*pi*r2*L;
%Now we will calculate the individual thermakl resistance network
Rconv1=1/(h1*A1);
R1=log(r2/r1)/(2*pi*k*L);
R2=log(r3/r2)/(2*pi*k2*L);
Rconv2=1/(h2*A2);
fprintf('Here are the values for your thermal resistance network')

Here are the values for your thermal resistance network

%pause(2);
fprintf('Rconv1= %6.3f C/W\n',Rconv1);

Rconv1=  0.000 C/W

%pause(2);
fprintf('R1= %6.3f C/W\n', R1);

R1=  0.000 C/W

%pause(2);
fprintf('R2= %6.3f C/W\n',R2);

R2=  0.532 C/W

%pause(2);
fprintf('Rconv2= %6.3f C/W\n',Rconv2);

Rconv2=  0.000 C/W

%Now we will add up the total thermal resistance
R=Rconv1+R1+R2+Rconv2;
%pause(5);
fprintf('Your total thermal resistance is %6.3f C/W.\n',R);

Your total thermal resistance is  0.532 C/W.

%Calculate the rate of heatloss
Qdot=(T1-T2)/R;  %W
%pause(3);
fprintf('Your rate of heat loss through our pipe, as spec''d, will\nbe %6.3f W per meter of pipe.\n',Qdot);

Your rate of heat loss through our pipe, as spec'd, will
be 798.472 W per meter of pipe.

%pause(3);
Qtotal=Qdot*L;
fprintf('Total heat loss through the pipe will be %6.3f W.\n', Qtotal);

Total heat loss through the pipe will be 798.472 W.

Tdrop=Qdot*R1;
fprintf('The drop in temperature along the pipe will be %6.3f degrees C.\n',Tdrop);

The drop in temperature along the pipe will be  0.242 degrees C.

figure(1)
plot(Qdot,T1,'bs:');
title('Qdot verses T1');
xlabel('Qdot');
ylabel('T1');

Answer 2

[Voss]

Don't use == for comparing character vectors; use strcmp (or strcmpi), e.g.:

if strcmp(pipe,'copper')
    
elseif strcmp(pipe,'stainless steel')
    
    % etc.
    
end

if strcmp(insulation,'glass wool')
    
    % etc.
    
end

Or use switch/case rather than if strcmp ... elseif strcmp ... elseif strcmp ...

switch pipe
    case 'copper'
        
    case 'stainless steel'
        
    % etc.
    
end

switch insulation
    case 'glass wool'
        
    % etc.
    
end

https://www.mathworks.com/help/matlab/ref/strcmp.html

https://www.mathworks.com/help/matlab/ref/switch.html

[Voss]

The reason you don't want to use == with character vectors is that == performs element-by-element comparison whether the arguments are numeric or characters.

% for numeric vectors:
[1 2 3] == [1 2 3] % returns a 1-by-3 vector of trues

ans = 1×3 logical array
   1   1   1

[1 2 3] == [1 5 3] % returns [true false true]

ans = 1×3 logical array
   1   0   1

% similarly, for character vectors (each character is an element):
'abc' == 'abc' % returns a 1-by-3 vector of trues

ans = 1×3 logical array
   1   1   1

'abc' == 'aec' % returns [true false true]

ans = 1×3 logical array
   1   0   1

So the two things being compared must be the same size (or one can be a scalar).

% if they are different sizes, you get an error:
[1 2 3] == [1 2 3 4] % error

Arrays have incompatible sizes for this operation.

'abc' == 'abcd' % error

[Jaevon Stewart]

Thank you! Your answer helped alot. I ended up using isequal(pipe,'copper') because I did not see the first part of your answer at first, but that worked for the code.

[Jaevon Stewart]

strcmp worked 20x better. Thank you.

[Voss]

You're welcome! Let me know if you have any questions. Otherwise, please "Accept" this Answer. Thanks!