Undefined function 'mtimes' for input arguments of type 'function_handle' in matlab app 2021

Question

I meet this error in matlab app design 2021 but when I use this function in editor, it work normal.

Thank you for your help.

Undefined function 'mtimes' for input arguments of type 'function_handle'.

Error in chiadoi (line 6) if((f(a)) * (f(c)) < 0)

this is my function

function [nghiem,solanlap] = chiadoi(f,a,b,saiso)
solanlap = 0;
syms x;
while(1)
    c = (a + b)/2;
    if((f(a)) * (f(c)) < 0)
        b = c;
    else
        a = c;
    end
    e = b - a;
    if(e < saiso)
        c = (a + b)/2;
        nghiem = c;
        fprintf("\nnghiem = %f",nghiem);
        fprintf("\nso lan lap = %d\n",solanlap);
        break;
    else
        solanlap = solanlap + 1;
    end
end
end

This is my code in app designer

f=app.nhaphamEditField.Value;
            f = str2func(['@(x)',f])
            a=app.nhapaEditField.Value;
            b=app.nhapbEditField.Value;
            saiso=app.nhapsaisoEditField.Value;
            g=app.hamlapEditField.Value;
            if(app.lapButton.Value)
                [nghiem,solanlap] = lap(f,g,a,b,saiso);
            elseif(app.chiadoiButton.Value)
                [nghiem,solanlap] = chiadoi(f,a,b,saiso);
            else
                [nghiem,solanlap] = tieptuyen(f,a,b,saiso);
            end
            app.nghiemEditField.Value=num2str(nghiem);
            app.solanlapEditField.Value=num2str(solanlap);
            plot(app.UIAxes,f);

I tried replace f(a) with fa and f(c) with fc but it dont work