Help with this MATLAB GUI code

I'm writing a code for a GUI program and there's something I can't get around.

M = str2double(get(handles.Input_M,'String'));
n = str2double(get(handles.Input_n,'String'));
Vx = str2double(get(handles.Input_Vx,'String'));
Dx = str2double(get(handles.Input_Dx,'String'));
Dy = str2double(get(handles.Input_Dy,'String'));
Dz = str2double(get(handles.Input_Dz,'String'));
t = str2double(get(handles.Input_3D_t,'String'));
X = str2double(get(handles.Input_3D_x,'String')); %%%error
Y = str2double(get(handles.Input_3D_y,'String')); %%%error
Z = str2double(get(handles.Input_3D_z,'String'));

[X,Y] = meshgrid(-10:0.1:10);

C = ((M./n)./(8).*((3.14.*t).^1.5).*sqrt(Dx.*Dy.*Dz)).*exp((-((X-Vx.*t).^2)./4.*Dx.*t)-(Y.^2/4.*Dy.*t)-(Z.^2./4.*Dz.*t)); %%%equation

contour3(X,Y,C,100)

I let the user input the variables for the equation which will generate a 3D contour. However for X and Y i get the red squiggly line that says "The value assigned to variable X might be unused".

So when I test the program, each different variable would change the contour in someway, however no matter what value I put for X or Y the contour doesn't change! Any ideas?

Answer 1

[Grzegorz Knor]

In this line:

[X,Y] = meshgrid(-10:0.1:10);

You overwrite X and Y.

[Bastion]

What do you mean? And how?

[Grzegorz Knor]

You load the variables X and Y from handles structure:

X = str2double(get(handles.Input_3D_x,'String')); %%%error

Y = str2double(get(handles.Input_3D_y,'String')); %%%error

And then, a few lines below, you overwrite them by:

[X,Y] = meshgrid(-10:0.1:10);

So regardless of the contents of the fields handles.Input_3D_y and handles.Input_3D_x, variables X & Y will not change.

[Bastion]

I see how do you propose I get around that?

I tried putting the input after that line but all I get is error.

[Grzegorz Knor]

I don't see the code, therefore I can only guess what the variables X and Y mean.

Could you explain it:

X = str2double(get(handles.Input_3D_x,'String'));

Y = str2double(get(handles.Input_3D_y,'String'));

?

[Jan]

@Bastian: The solution is trivial: You have to rename einer the first or the second definition of X and Y.

If you write "X=3; X=4" the first definition is overwritten and MLint warns for that (so this is *not* an error! It is only mostlikely not wanted).

[Bastion]

@Grzegorz:

X and Y are just variables in the equation C, I want the user to input any number they want and then generate a contour3 plot with X, Y and C as the axis.

[Bastion]

@Jan:

Yes I understand this but how do I do it?

[Grzegorz Knor]

If X and Y will be a scalar values, then C also will be a scalar, and you will not be able to draw a contour plot.

[Bastion]

How do I change this? Use ()?

Answer 2

[Jan]

After your comment to Grzegorz's answer:

I'm deeply confused about your question, how you could do this. The problem is, that you overwrite an existing definition equivalent to:

X = 3;
X = 4;

You can avoid this by renaming on of the variables, e.g.:

X1 = 3;
X = 4;

Or:

X = 3;
X2 = 4;

But this is trivial and the program you've posted looks like you have enough programming skills to find this by your own.

The user can "input any number" for X and Y, so let's assume it is 19 in both cases. Now, how do you want this number to be used "as axis"? Currently you overwrite the values by "[X,Y] = meshgrid(-10:0.1:10);". Perhaps you want something like:

X = linspace(-X, X, 100);

Or:

X = -X:0.1:X

[Bastion]

Yes that's what I want I guess, the X and Y defining the dimensions and as variables.

I'm actually only a beginner in Matlab GUI and all I'm doing is looking up the Help guide, not very helpful.

So the meshgrid() is basically setting out the dimensions in my plot? But it's overridding my values, I would be better off with linspace()?

Answer 3

[Bastion]

I tried some of the suggestions but I can't seem to generate a contour anymore. Any ideas?