How to pass an output from a function to be processed in another function

So i have a function that inputs coordinates and plots a line

 function linetranslation(xa,ya,xb,yb)
if nargin == 0
    xa = input('First X Coordinate  : ');
    ya = input('First Y Coordinate  : ');
    xb = input('Second X Coordinate : ');
    yb = input('Second Y Coordinate : ');
  
end
clf;
hold on;
axis([-10 10 -10 10]);
if xa==xb
   if ya<yb
      for yi=ya:0.01:yb;
    xi=yi+xa-yi;
    plot(xi,yi);    
      end
   else
      for yi=ya:-0.01:yb;
    xi=yi+xa-yi;
    plot(xi,yi);
      end
   end
else
   m=(yb-ya)/(xb-xa);
   if xa<xb
      for xi=xa:0.01:xb;
          yi=m*(xi-xa)+ya; 
          plot(xi,yi);
      end
   else
      for xi=xa:-0.01:xb;
          yi=m*(xi-xa)+ya;
          plot(xi,yi);
      end
   end
end
end

the question is how can i pass xi & yi to another function that processes it further

a little idea here, i have tried adding to the first function

 function [xi, yi] = linetranslation(xa,ya,xb,yb)

and adding the code below

 function Translate(x,y)
>>>here [xi , yi] = linetranslation(xa,ya,xb,yb);
if nargin == 0
    % Check the number of input arguments (nargin)
    x  = input('Translate X: ');
    y  = input('Translate Y: ');
 end

 hold on;
 axescenter
 axis([-10 10 -10 10]);
 plot(xi+x,yi+y);

but it returns xa undefined, on the other hand i need xi and yi to be passed

thanks in advance

UPDATE

i have tried putting

 [xi,yi] = translasigaris;

below

 function translate(x,y)

but

 if nargin == 0
    xa = input('First X Coordinate  : ');
    ya = input('First Y Coordinate  : ');
    xb = input('Second X Coordinate : ');
    yb = input('Second Y Coordinate : ');
  
end

returns as an infinite loop.

Answer 1

[Star Strider]

If you want to make ‘xi’ and ‘yi’ available to other functions, the easiest way is to have your ‘linetranslation’ function output them.

Change your original function statement to:

function [xi,yi] = linetranslation(xa,ya,xb,yb)

When you then call it such as in this statement:

[xi,yi] = linetranslation(xa,ya,xb,yb);

‘xi’ and ‘yi’ (by whatever variable names you want to assign them to) will be available in your workspace.

[Monty Ramadhan]

i have tried putting

 [xi,yi] = linetranslation(xa,ya,xb,yb);

in function translate right below

 function Translate(x,y)

but it still returns 'xa' is undefined

and when i put

[xi,yi] = linetranslation;

under

 function Translate(x,y)

it returns this code below as an infinite loop

 if nargin == 0
    xa = input('First X Coordinate  : ');
    ya = input('First Y Coordinate  : ');
    xb = input('Second X Coordinate : ');
    yb = input('Second Y Coordinate : ');
  
end

[Star Strider]

If you don’t supply your function with any input arguments, the nargin function will always evaluate to zero. Nothing you can do inside the function will change that.

One way around that would be to have another if block:

if nargin == 0
    argnr = 0;
end
if argnr == 0
    xa = input('First X Coordinate  : ');
    ya = input('First Y Coordinate  : ');
    xb = input('Second X Coordinate : ');
    yb = input('Second Y Coordinate : ');
    argnr = 1;
end

However I would completely delete this if block:

if nargin == 0
    xa = input('First X Coordinate  : ');
    ya = input('First Y Coordinate  : ');
    xb = input('Second X Coordinate : ');
    yb = input('Second Y Coordinate : ');
end

First, because anything you enter there is going to overwrite whatever you pass as arguments to your function, and...

Second, because MATLAB will throw a ‘not enough input arguments’ error if you don’t pass all of them and you don’t have a nargin check.

The solution is to:

1. Delete the current if block,
2. Pass all the arguments to the function in your script,
3. Return the arguments you want as your function outputs.

[Monty Ramadhan]

i want the user to input the variables to the function and pass the output arguments, is there a solution?

could you give me the example?

[Star Strider]

If you want the user to input the information interactively using input-type statements within the function and not pass them as arguments, I would do this:

function [xi,yi] = linetranslation()

so there are no input arguments, then instead of the if block and your input lines, replace them with this code to use a GUI to input the coordinates:

dlg_title = 'Enter Coordinates:';
prompt = {'First X Coordinate:','First Y Coordinate:','Second X Coordinate:','Second Y Coordinate:'};
coords = inputdlg(prompt, dlg_title,[1 45; 1 45; 1 45; 1 45]);
[xa,ya,xb,yb] = deal(str2num(char(coords)));

It’s easier to work with than the Command Window input function, and doesn’t clutter the Command Window.

The dialog box looks like this:

It works like any other dialog box, and returns the ‘xa’, ‘ya’, ‘xb’, ‘yb’ as numbers in the deal call in the line that follows the ‘coords’ assignment. Use them in your code exactly as you do now. The function will then return [xi,yi] as you want.

[Monty Ramadhan]

okay so i've modified my code by replacing the function header with yours

and replacing the if input block with your GUI input dialogue

when i input coordinates with my if block which is 1,1,1,5

i get

when i input with my if nargin block i get

and the second function still calls the dialogue for looping even when

 function [xi,yi] = linetranslation() %is empty

[Star Strider]

Use this:

dlg_title = 'Enter Coordinates:';
prompt = {'First X Coordinate:','First Y Coordinate:','Second X Coordinate:','Second Y Coordinate:'};
coords = inputdlg(prompt, dlg_title,[1 45; 1 45; 1 45; 1 45]);
[xa,ya,xb,yb] = coords{:};
xa = str2num(xa);
ya = str2num(ya);
xb = str2num(xb);
yb = str2num(yb);

It will work.

[Monty Ramadhan]

thank you! it did work!, but it still loops the dialogue in the second

and didnt pass the output arguments, when i closed the dialogue it returns this error

[Star Strider]

My pleasure!

I need to see your complete code for your ‘linetranslation’ function in order to see what’s wrong.

Also by calling it as:

linetranslation

you will only get ‘xi’. You have to call it as:

[xi,yi] = linetranslation

to get both outputs.

[Monty Ramadhan]

first of all thankyou for helping me and here's my 'linetranslation' code

 function [xi,yi] = linetranslation() 

 dlg_title = 'Enter Coordinates:';
prompt = {'First X Coordinate:','First Y Coordinate:','Second X Coordinate:','Second Y Coordinate:'};
coords = inputdlg(prompt, dlg_title,[1 45; 1 45; 1 45; 1 45]);
[xa,ya,xb,yb] = coords{:};
xa = str2num(xa);
ya = str2num(ya);
xb = str2num(xb);
yb = str2num(yb);

 clf;
hold on;
axis([-10 10 -10 10]);
if xa==xb
   if ya<yb
      for yi=ya:0.01:yb;
    xi=yi+xa-yi;
    plot(xi,yi);
      end
   else
      for yi=ya:-0.01:yb;
    xi=yi+xa-yi;    
    plot(xi,yi);
      end
   end
else
   m=(yb-ya)/(xb-xa);
   if xa<xb
      for xi=xa:0.01:xb;
      yi=m*(xi-xa)+ya; 
    plot(xi,yi);   
    plot(xi,yi);    
      end
   else
      for xi=xa:-0.01:xb;
      yi=m*(xi-xa)+ya;
    plot(xi,yi);    
    plot(xi,yi); 
      end
   end
end
axescenter
translate

and this is my 'translate' function

 function translate(x,y)
 [xi,yi] = linetranslation();
 dlg_title = 'Enter Coordinates:';
 prompt = {'Translate X:','Translate Y:'};
 coords = inputdlg(prompt, dlg_title,[1 45; 1 45]);
 [x,y] = coords{:};

 hold on;
 axescenter

 axis([-10 10 -10 10]);
 plot(xi+x,yi+y);

the code axescenter refers it to this file here

axescenter

[Star Strider]

My pleasure!

I haven’t run your code with ‘translate’, because I believe one of your problems is that inputdlg returns a cell, and the following line:

[x,y] = coords{:};

deals the two inputs to ‘x’ and ‘y’ respectively, as desired. They are however character representations of the numbers entered in inputdlg, so you have to add these lines:

x = str2num(x);
y = str2num(y);

just after the inputdlg call to convert the strings to actual double-precision numbers.

See if that improves things.

Also, if you’re not going to pass (x,y) to ‘translate’ as input arguments (entering them within the function using inputdlg), avoid confusion and define it as:

function translate()

instead.

I have ‘axiscenter’. It’s one of Matt Fig’s brilliant contributions.

[Monty Ramadhan]

silly me, i've forgot about adding the string to number conversion. Right.., so i changed the function header of 'translate' and added the conversion, and it still returns the same error as the image i've posted above. i'm really wondering why it returns this error when i call 'translate' from 'linetranslation'

 ??? Reference to non-existent element of a cell array.

 Error in ==> linetranslation at 6 
[xa,ya,xb,yb] = coords{:};

 Error in ==> translate at 2
[xi,yi] = linetranslation();

[Star Strider]

The code I provided works, and it apparently worked before. I don’t know why it’s not working now in your code.

Remove the semicolons from all the inputdlg calls and see what the result is.

[Monty Ramadhan]

My mistake, the function 'linetranslation' works fine, but when running it with 'translate' by adding it under 'axescenter' it loops the dialogue from 'linetranslation' and returns the error above when i close it

this is my 'translate' function as it is now

 function translate()
 [xi,yi] = linetranslation();
 dlg_title = 'Enter Coordinates:';
 prompt = {'Translate X:','Translate Y:'};
 coords = inputdlg(prompt, dlg_title,[1 45; 1 45]);
 x = str2num(x);
 y = str2num(y);

 hold on;
 axescenter
 axis([-10 10 -10 10]);
 plot(xi+x,yi+y);

[Star Strider]

The easiest way to solve that problem is to not call ‘linetranslation’ from within ‘translate’. Do this instead:

1. Take the ‘linetranslation’ call out of ‘translate’,
2. Put (x,y) input arguments into ‘translate’,
3. Call ‘linetranslation’ first,
4. Consider wrapping both functions in another function file, depending on what you want to do with theses functions.

Make appropriate changes to the initial lines of your functions so that you can use them this way:

[xi,yi] = linetranslation
translate(xi,yi)

That should solve your problem. Sometimes, nesting functions such as you did, with potentially interfering inputdlg calls simply won’t work. You might consider using clf after the str2num calls, since UI objects are considered figures (or at least they were before R2014b), but I can’t guarantee that will work.

I have no other suggestions. See if the sequential call idea works.

[Monty Ramadhan]

thanks for helping, i'll figure out something for the moment.

Is there any way to pass the arguments with a different method? using classes maybe?

I've found an interesting link here ,

Capture Data Values For Later Use By a Function

i'm new at 'MATLAB' so i'm having quite a difficult time understanding the method formats

[Star Strider]

My pleasure!

I’m not sure how the ideas in that link would help you. The data already have to exist in the workspace for that to work, and in your situation, they do not.

I would simply enter all the data in your main program (using inputdlg), pass it to ‘linetranslation’ through its input argument list as data, then pass the data returned by ‘linetranslation’ to ‘translate’ in its input argument list, as I illustrated earlier.

Using inputdlg from within your functions as you are, you’re making a relatively simple problem difficult to the point that it may have no workable solutions.

[Monty Ramadhan]

thanks!, i've modified my code so that the function 'linetranslation' plots 'xi' and 'yi' and plot 'xj' and 'yj' which is

 xj=xi+x;
 yj=yi+y;

As you suggested i nested 'translate' within 'linetranslation' and share the variables 'xj' and 'yj', now it plots 2 line from 'linetranslation', after plotting the lines i've modified it to call 'translate' and calling another input dialogue inside the function.

What i hope to achieve now is that the user could translate the second line from the 'linetranslation' function which is 'xj' and 'yj', this is my modified code in one m file.

The function does not returns any errors, but the problem is that function 'translate' doesn't plot a new line in the figure after executed, please review my code and thanks in advance, i think i might have made a stupid mistake somewhere

 function [xj,yj] = linetranslation()

 dlg_title = 'Enter Coordinates:';
 prompt = {'First X Coordinate:','First Y Coordinate:','Second X   Coordinate:','Second Y Coordinate:','X Translation','Y Translation'};
 coords = inputdlg(prompt, dlg_title,[1 45; 1 45; 1 45; 1 45; 1 45; 1 45]);
 [xa,ya,xb,yb,x,y] = coords{:};
 xa = str2num(xa);
 ya = str2num(ya);
 xb = str2num(xb);
 yb = str2num(yb);
 x  = str2num(x);
 y  = str2num(y);
 clf;
 axescenter
 hold on;
 axis([-10 10 -10 10]);
 if xa==xb
   if ya<yb
      for yi=ya:0.01:yb;
    xi=yi+xa-yi;
      xj=xi+x;
      yj=yi+y;
    plot(xi,yi);
    plot(xj,yj,'r');
      end
   else
      for yi=ya:-0.01:yb;
    xi=yi+xa-yi;
    xj=xi+x;
    yj=yi+y;    
    plot(xi,yi);
    plot(xj,yj,'r');
      end
   end
 else
   m=(yb-ya)/(xb-xa);
   if xa<xb
      for xi=xa:0.01:xb;
      yi=m*(xi-xa)+ya;
    xj=xi+x;
    yj=yi+y;    
    plot(xi,yi);
    plot(xj,yj,'r');
      end
   else
      for xi=xa:-0.01:xb;
      yi=m*(xi-xa)+ya;
    xj=xi+x;
    yj=yi+y;    
    plot(xi,yi);
    plot(xj,yj,'r');
      end
   end
 end
 function translate()
 dlg_title = 'Enter Coordinates:';
 prompt = {'Translate X:','Translate Y:'};
 coords = inputdlg(prompt, dlg_title,[1 45; 1 45]);
 [a,b] = coords{:};
 a = str2num(a);
 b = str2num(b);

 hold on;
 axescenter
 axis([-10 10 -10 10]);
 plot(xj+a,yj+b);
 end
 translate(xj,yj);
 end

[Star Strider]

Save the quantities you want to plot in an array and then plot them after the loop. Plotting inside an iterating loop will likely not give you the result you want.

[Monty Ramadhan]

could you give me an example or reference?

[Star Strider]

Initialise a counter just before the start of your if blocks, for instance:

k = 1;
if xa==xb                % Start Of Outer ‘if’ Block

then in your loop, set new variables, for instance ‘fx’ and ‘fy’ and set:

fx(k) = xj+a;            % The last time you calculate ‘xj+a’ In Loop
fy(k) = yj+b;            % The last time you calculate ‘yj+b’ In Loop

then just before the end of the loop, add:

k = k+1;
end                      % Last Statement In Loop

then after the loop:

figure
plot(fx, fy)
axis([-10  10    -10  10])

[Monty Ramadhan]

thanks for bearing with my questions. Yes, i've proved your point where you said that it won't give the results i wanted. I made a new file without the if blocks and it passes the arguments from the parent function to the nested functions just fine. Just to clarify the example in your post, is this what you mean?

 k = 1;
 if xa==xb
   if ya<yb
      for yi=ya:0.01:yb;
      xi=yi+xa-yi;
      xj(k)= xi+a;
      yj(k)= yi+b;
      k = k+1;
      end
      axescenter
      plot(xi,yi);
      plot(xj,yj);
      axis([-10 10 -10 10]);

[Star Strider]

I doubt plotting ‘xi’ and ‘yi’ would work, since they still seem to be single values, and they will be the last values they had at the end of the loop.

You are correct on the other plot call however. This is what I intended:

. . . CODE . . .
xj(k)= xi+a;
yj(k)= yi+b;
. . . CODE . . .
plot(xj,yj);
axis([-10 10 -10 10]);

[Monty Ramadhan]

Yes, it returns xi & yi as a point on the figure not as a line as i intended. How i can manage this to pass the variables inside the loop to the nested function?

[Star Strider]

Subscript them as well.

[Monty Ramadhan]

subscript? as what you did with xj & yj?

[Star Strider]

Yes.

[Monty Ramadhan]

First of all, thankyou for commenting back and your patience guiding me.

I have a feeling that this is going to be done soon! the line shows in the figure and it calls 'translate' brilliantly! but a little problem when i subscript xi & yi, the lines comes out as a diagonal line, but xj & yj comes out vertical as my inputs are 'xa,ya,xb,yb' are '1,1,1,5' and the translations as shown in the image below, the third line which is located in the nested function 'translate' is 'xk' & 'yk' and it shows the line brilliantly as i intended it to be, the only problem now is 'xi' and 'yi' it self

as my if block code is now

k = 1;
if xa==xb
 if ya<yb
    for yi=ya:0.01:yb;
    xi=yi+xa-yi;
    xj(k)= xi+x;
    yj(k)= yi+y;
    xi(k)= xi;
    yi(k)= yi;
    k = k+1;
    end
    plot(xi,yi);
    plot(xj,yj,'r');

[Star Strider]

My pleasure!

I don’t understand this:

xi=yi+xa-yi;

since it’s equivalent to:

xi = xa;

I don’t know how your calculate ‘xa’ or ‘yi’, or the reason you’re plotting them. If ‘xj’ and ‘yj’ work as you want them to, isn’t that enough? Besides, if ‘xi’ and ‘yi’ are translation functions, it would stand to reason that they would plot as a slanted line reflecting the translation you want them to perform.

[Monty Ramadhan]

The original code was intended just to plot a line in matlab, since i've found it that way and it works fine, i didn't bother to change it a bit, but since you've mentioned it, i've applied it to my code, and it works fine!, so thankyou once again. Yes 'xi' and 'yi' are translation functions, but the slanted line it plotted was not what i intend my application to plot, but thanks to your guide and patience i have achieved what i wanted.

What i wanted to achieve is to transform again the line that i've transformed and plotted , and i think i've achieved it, i have tested it and haven't found any bugs yet, if it's not trouble some i would like you to test the code, it's a fully running code, please tell me of flaws and bugs that you found.

Once again, Thankyou.

[Star Strider]

My pleasure!

If your code does what you want and you’re happy with it, that works for me!

Answer 2

[Abhiram Bhanuprakash]

Hi Monty,

I think one way of solving this would be to use a kind of 'main' function.

You may name it whatever you like, for example, let's say, 'translate_main'.

It can be something like this:

function translate_main(xa,ya,xb,yb)

if nargin == 0
    xa = input('First X Coordinate  : ');
    ya = input('First Y Coordinate  : ');
    xb = input('Second X Coordinate : ');
    yb = input('Second Y Coordinate : ');
  
end

[xi, yi] = linetranslation(xa,ya,xb,yb);

Translate(xi,yi); % This passes the output of linetranslation as input to Translate

end

And, as you have mentioned, the function linetranslation can be declared as:

function [xi, yi] = linetranslation(xa,ya,xb,yb)

and the function Translate can be declared as:

function Translate(x,y)

From the Command Window, you can call translate_main as:

translate_main(xa,ya,xb,yb);

where xa,ya,xb,yb are defined previously in the MATLAB base workspace.

Hope this helps,

Cheers!

Abhiram.

[Monty Ramadhan]

hi Abhiram, thanks for the answer, but that's not what i'm looking for. I'm trying to process xi & yi from the second function (Translate) which is a different .m file, i'm sorry i didnt mention this before.