How to define a variable?

Question

Veronika 2015-1-30

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/173636-how-to-define-a-variable

编辑： per isakson 2015-2-1

Dear all,

I have this code:

    prompt = {'Type the value j:'};
    dlg_title = 'Create your own model';
    num_lines = 1;
    j = 0.5;
    def = {'0.5'};
    answer = inputdlg(prompt,dlg_title,num_lines,def);
    imdl =  mk_common_model('d2d1c',16);
    img_1 = mk_image(imdl);
    figure
    show_fem(img_1);
    img_2 = img_1;
    ['x-' num2str(j) '.^2+ (y- 0.5) .^2<0.1^2, ''x,'  'y,'  'z']
    select_fcn = inline('(x-j).^2+(y-0.5).^2<0.1^2','x','y','z')
    img_2.elem_data = 1 + elem_select(img_2.fwd_model, select_fcn);
    figure
    show_fem(img_2);
    vh = fwd_solve(img_1);
    vi = fwd_solve(img_2);

I have a problem with variable j. I want to change my inline function, for example user enters j = 0.1 so my inline function should look like (x-0.1).^2+(y-0.5).^2<0.1^2','x','y','z'. But Command Window returns this:

ans =
x-0.5.^2+ (y- 0.5) .^2<0.1^2, 'x,y,z
select_fcn =
       Inline function:
       select_fcn(x,y,z) = (x-j).^2+(y-0.5).^2<0.1^2

Does anyone know where is the mistake?

Thank you for your ideas.

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Veronika 2015-1-31

编辑：per isakson 2015-2-1

在 MATLAB Online 中打开

So I rewrote the inline function to an anonymous function. And I rewrote the variable j to the variable p. Now, I have this code:

   prompt = {'Napište hodnotu p:'};
dlg_title = 'Vytvoření vlastního modelu';
num_lines = 1;
p = 0.5;
def = {'0.5'};
answer = inputdlg(prompt,dlg_title,num_lines,def);
imdl =  mk_common_model('d2d1c',16);
img_1 = mk_image(imdl);
figure
show_fem(img_1);
img_2 = img_1;
['x-' num2str(p) '.^2+ (y- 0.5).^2<0.1^2']
select_fcn = @(x,y) (x-p).^2+(y-0.5).^2<0.1^2;
img_2.elem_data = 1 + elem_select(img_2.fwd_model, select_fcn);
figure
show_fem(img_2);
vh = fwd_solve(img_1);
vi = fwd_solve(img_2);

But Comand Window returns this:>> GUI

ans =
x-0.5.^2+ (y- 0.5).^2<0.1^2
Error using C:\Users\Veronika\Desktop\BP\GUI.m>@(x,y)(x-p).^2+(y-0.5).^2<0.1^2
Too many input arguments.
Error in elem_select (line 57)
    memb_frac = mean( feval(select_fcn,x,y,z), 2);
Error in GUI>pushbutton5_Callback (line 115)
img_2.elem_data = 1 + elem_select(img_2.fwd_model, select_fcn);
Error in gui_mainfcn (line 96)
        feval(varargin{:});
Error in GUI (line 42)
    gui_mainfcn(gui_State, varargin{:});
Error in @(hObject,eventdata)GUI('pushbutton5_Callback',hObject,eventdata,guidata(hObject))
Error while evaluating uicontrol Callback

My release of Matlab is MATLAB R2011b.

Stephen23 2015-1-31

编辑：Image Analyst 2015-1-31

在 MATLAB Online 中打开

And what kind of an object is img_2.fwd_model ?

At this point I think your best bet would be to start using the debugger , and set a breakpoint inside the Anonymous function.

You could also try this anonymous function instead:

select_fcn = @(varargin)disp(nargin);

Just to see how many inputs it is getting. But the debugger is going to be your best tool for solving this.

Veronika 2015-1-31

编辑：Image Analyst 2015-1-31

img_2.fwd_model is figure of the conductivity based on the function (x-p).^2+(y-0.5).^2<0.1^2.

Ok, I try debugger.

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Answer 1

per isakson 2015-2-1

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/173636-how-to-define-a-variable#answer_166557

编辑：per isakson 2015-2-1

在 MATLAB Online 中打开

"[...]changing variable p whichever user inserts" &nbsp I assume "*z*" is a highlighted input variable. However, I cannot find any comment on "*z*".

The anonymous function (function handle) includes a "snapshot" of the current workspace of the moment when it is created. In your case p with the value 0.5 is stored in select_fcn. Later changes of the value of p doesn't doesn't affect select_fcn.

Proposal: replace

select_fcn = @(x,y, *z* ) (x-p).^2+(y-0.5).^2<0.1^2;

by

select_fcn = @(x,y,p) (x-p).^2+(y-0.5).^2<0.1^2;

&nbsp

"Error in elem_select (line 57) memb_frac = mean( feval(select_fcn,x,y,z), 2);" &nbsp Comments:

feval(select_fcn,x,y,z) select_fcn is defined with two input arguments, @(x,y)
feval is not required to evaluate an anonymous function. Replace feval(select_fcn,x,y,z)) by select_fcn(x,y,z)

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Veronika 2015-2-1

编辑：per isakson 2015-2-1

Thank you for your answer.

I rewrote z to p, but nothing changed, still returns me to a value of 0.5 rather than a user specified value.
And for the second error, I do not know where I have to change that select_fcn(x,y,z), because I can´t see it in my code.

per isakson 2015-2-1

编辑：per isakson 2015-2-1

在 MATLAB Online 中打开

What is the intended role of z in

select_fcn = @(x,y,z) (x-p).^2+(y-0.5).^2<0.1^2;

z is input, but not used. Why?

I looked at the EIDORS page, but that didn't help much. I didn't give it the time needed. My conclusions:

EIDORS is a large toolbox, which is 10++ years old. Anonymous functions didn't exist in Matlab at that time. (However, the current release is only a year old.)
You try to call the function elem_select with a set of input arguments that doesn't honor the documentation. No surprise an error is thrown.
You did not provide this context in your question and thus it was hard to give useful answers.

"because I can´t see it in my code" &nbsp That's because elem_select (The name is in the error message.) is a function in the EIDORS toolbox.

&nbsp

It is not a good idea to modify code in the EIDORS toolbox. Thus, it remains to adhere to the documentation of EIDORS. (We may trust The MathWorks that inline can be replaced by anonymous functions.) The definition of the anonymous function must be like

select_fcn = @(x,y,z) (x-0.5).^2+(y-0.5).^2<0.1^2;

EIDORS doesn't say one may add an extra input argument. That's mean one cannot.

&nbsp

One solution is to redefine the anonymous function for each new value of p.

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