May I know why 'value must be a double scalar' come out in app designer?

syms x

f_bisection = app.EquationEditField.Value;

f2_bisection = str2sym(f_bisection);

a=app.aEditField.Value;

b=app.bEditField.Value;

iteration=1;

itemax = 70;

if f_bisection(a)*f_bisection(b)>0

disp('Wrong choice')

else

x=(a+b)/2;

while iteration < itemax

if f_bisection(a)*f_bisection(x)<0

b=x;

else

a=x;

end

x=(a+b)/2;

iteration=iteration+1;

end

end

app.RootEditField.Value = x;

Answer 1

[Nivedita]

Hello Aqilah!

I understand that you are receiving the error “ 'Value' must be a double scalar” in app designer.

I am assuming that this error is thrown for the last line:

app.RootEditField.Value = x;

There are two types of edit fields in app designer: numeric and text. Numeric edit fields only receive double scalar values. Since “x” is a symbolic variable, MATLAB is rejecting the value and throwing the error.

You can convert “x” into a double scalar using the “double” function and assign it to “RootEditField” in the following manner:

app.RootEditField.Value = double(x);

For more information on the “Value” property of “NumericEditFields” in app designer and the “double” function, you can refer to the following documentation links:

1. NumericEditField.Value: https://www.mathworks.com/help/releases/R2021b/matlab/ref/matlab.ui.control.numericeditfield-properties.html#:~:text=Value%20%E2%80%94%20Value%20in%20edit%20field
2. double: https://www.mathworks.com/help/releases/R2021b/symbolic/double.html

I hope this helps!

Regards,

Nivedita.