Error using sym>convertChar

Error using sym>convertChar

Character vectors and strings in the first argument can only specify a variable or number. To evaluate character vectors and strings

representing symbolic expressions, use 'str2sym'.

Error in sym>tomupad (line 1608)

S = convertChar(x);

Error in sym (line 400)

S.s = tomupad(x);

Error in sym/privResolveArgs (line 1180)

argout{k} = sym(arg);

Error in sym/diff (line 29)

args = privResolveArgs(S, invars{:});

Error in NEWTONRAPHSON/STARTButtonPushed (line 39)

df = diff(app.fun,x);

Error in matlab.apps.AppBase>@(source,event)executeCallback(appdesigner.internal.service.AppManagementService.instance(),app,callback,requiresEventData,event) (line 63)

newCallback = @(source, event)executeCallback(appdesigner.internal.service.AppManagementService.instance(), ...

Error while evaluating Button PrivateButtonPushedFcn.

HOW DO I SOLVE THIS PROBLEM

[KSSV]

Show us your code.

[CHUNG SI HAO]

syms x

df = diff(str2sym(app.fun,x));

app.dfdxEditField.value = char(df) ;

%Initial start

xold = app.StartingpointEditField.Value;

for i=1:app.NoofIterationEditField.Value

x = xold;

Function = eval(app.fun);

Derivative = eval(df);

xnew = xold - Function/Derivative;

AbsErr = abs(xold - xnew);

app.UITable.Data(i,:) = [i xold xnew Function AbsErr];

xold = xnew;

if AbsErr <= app.ToleranceEditField.Value

break

end

pause(1);

end

[Walter Roberson]

eval() of a symbolic expression such as df has undefined results. You should never eval() anything symbolic. Use subs() instead.

[CHUNG SI HAO]

after i change eval() to subs()

it shows

Error using str2sym

Too many input arguments.

Error in NEWTONRAPHSON/STARTButtonPushed (line 39)

df = diff(str2sym(app.fun,x));

Error in matlab.apps.AppBase>@(source,event)executeCallback(appdesigner.internal.service.AppManagementService.instance(),app,callback,requiresEventData,event) (line 63)

newCallback = @(source, event)executeCallback(appdesigner.internal.service.AppManagementService.instance(), ...

Error while evaluating Button PrivateButtonPushedFcn.

[Walter Roberson]

df = diff(str2sym(app.fun),x);

[CHUNG SI HAO]

there is a new problem again

Error while evaluating Button PrivateButtonPushedFcn.

Unrecognized property 'value' for class 'matlab.ui.control.EditField'.

Error in NEWTONRAPHSON/STARTButtonPushed (line 40)

app.dfdxEditField.value = char(df) ;

Error in matlab.apps.AppBase>@(source,event)executeCallback(appdesigner.internal.service.AppManagementService.instance(),app,callback,requiresEventData,event) (line 63)

newCallback = @(source, event)executeCallback(appdesigner.internal.service.AppManagementService.instance(), ...

Error while evaluating Button PrivateButtonPushedFcn.

[Walter Roberson]

app.dfdxEditField.Value = char(df) ;

[CHUNG SI HAO]

i dont understand what u mean

[Walter Roberson]

Change line 40

app.dfdxEditField.value = char(df) ;

to become

app.dfdxEditField.Value = char(df) ;

Notice value with lower case becomes Value with upper case

[CHUNG SI HAO]

then it become like this

Error using sym>convertChar

Character vectors and strings in the first argument can only specify a variable or number. To evaluate character vectors and strings

representing symbolic expressions, use 'str2sym'.

Error in sym>tomupad (line 1608)

S = convertChar(x);

Error in sym (line 400)

S.s = tomupad(x);

Error in subs (line 66)

r_unique_name = evalin('caller',cmd_unique_name);

Error in NEWTONRAPHSON/STARTButtonPushed (line 46)

Function = subs(app.fun);

Error in matlab.apps.AppBase>@(source,event)executeCallback(appdesigner.internal.service.AppManagementService.instance(),app,callback,requiresEventData,event) (line 63)

newCallback = @(source, event)executeCallback(appdesigner.internal.service.AppManagementService.instance(), ...

Error while evaluating Button PrivateButtonPushedFcn.

[Walter Roberson]

change

                x = xold;
                Function = eval(app.fun);
                Derivative = eval(df);

to

Function = double(subs(str2sym(app.fun),x,xold));

Derivative = double(subs(df, x, xold)) ;

[Walter Roberson]

Have you considered how much easier it would be if you had stored str2sym of the function in app.fun instead of converting the text to symbolic all the time? And have you considered how much easier it would be to use matlabFunction?

[CHUNG SI HAO]

how to stored str2sym in app.fun

this my app.fun

properties (Access = private)

fun

end

[Walter Roberson]

At some point you have code similar to

app.fun = app.Editfield1.Value;

You would change that to

app.fun = str2sym(app.Editfield1.Value);

[CHUNG SI HAO]

Thank you Sir I got it