'Value' in App Designer must be a scalar of type double. How do I fix the error?

function ButtonPushed(app, event)

[UA, NTU, e, T_w, Q, Q_t, C_min] = Calculate(app);

clc

fprintf("UA = %g W/K\n",UA)

fprintf("NTU = %g\n",NTU)

fprintf("e = %g\n",e)

fprintf("냉각수 수렴 온도 = %g 'C\n",T_w)

fprintf("라디에이터 방열량 = %g kW\n",Q)

fprintf("C_min = %.2f\n", C_min)

%% 결과 도출 %%

app.Target_UA.Value = UA;

app.NoTU.Value = NTU;

app.Effective.Value = e;

app.Final_T_water.Value = T_w;

app.Q_Radiator.Value = Q;

if Q >= Q_t

app.Lamp.Color = [0.00,0.00,1.00];

app.Label_13.Text = "냉각";

else

app.Lamp.Color = [1.00,0.00,0.00];

app.Label_13.Text = "과열";

end

end

I wrote the ButtonPushed function code above in App Designer. As a result of checking the five clearly calculated variables using the 'fprintf' function, each appears as a real number scalar like

"UA = 8573.74 W/K

NTU = 14.4686

e = 0.999613

냉각수 수렴 온도 = 57.7925 'C

라디에이터 방열량 = 58.9937 kW

C_min = 0.59",

but I don't know why it keeps saying 'Value' in

"app.Target_UA.Value = UA;

app.NoTU.Value = NTU;

app.Effective.Value = e;

app.Final_T_water.Value = T_w;

app.Q_Radiator.Value = Q;"

must be a double scalar and it doesn't work. Is it a bug in the program itself?

Answer 1

[Ayush Modi]

Hi,

As per my understanding, you are returning the values from calculate function. It is not sufficient to print the values of the variable to check the datatype. "fprintf" function will display the values but not the type and there are multiple numerical datatypes in MATLAB.

You can explicitly convert the value to "double" datatype before assigning them to the 'Value' property. Here is an example to demonstrate how you can achieve this:

app.Target_UA.Value = double(UA);

Also, you can check the class of a variable using "class" function. Here is an example:

classname = class(UA)

Please refer to the following MathWorks documentation for more information on:

• Numeric datatypes supported by MATLAB: https://www.mathworks.com/help/matlab/numeric-types.html
• "class": https://www.mathworks.com/help/matlab/ref/class.html

I hope this helps!